CN110687153B - Compact sandstone reservoir pore mobility classification and evaluation method - Google Patents

Abstract

The invention relates to a compact sandstone reservoir pore mobility classification and evaluation method, which comprises the following specific steps: s1, preparing a sample, and performing nuclear magnetic resonance and high-pressure mercury injection test on the sample; s2, according to the mercury inlet saturation S _Hg And mercury feed pressure P _c Drawing a mercury intrusion curve, a Pittman curve and a fractal curve, determining the boundary of the inter-granular pores and the intra-granular pores according to the boundary of a 'platform segment' and an 'increasing segment' of the mercury intrusion curve, the vertex of the Pittman curve and the turning point of the fractal curve, and dividing the inter-granular pores and the intra-granular pores according to the boundary; s3, according to the relation between a saturated water nuclear magnetic curve and a bound water nuclear magnetic curve, combining the limits of inter-particle pores and intra-particle pores, dividing the inter-particle pores into movable macropores and isolated macropores, and dividing the intra-particle pores into movable micropores and unmovable micropores; and S4, calculating the contents of different types of pores. The method can realize the evaluation of the mobility of different types of pores of the compact sandstone reservoir, so that the mobility evaluation of the pores of the reservoir is more in line with the actual geological condition, and the evaluation result is more accurate.

Description

Classification and Evaluation Method of Pore Mobility in Tight Sandstone Reservoirs

technical field

The invention belongs to the technical field of oil and gas geological exploration, in particular to a method for classifying and evaluating pore mobility of tight sandstone reservoirs.

Background technique

Tight sandstone reservoirs have residual intergranular pores, dissolved pores and clay intercrystalline pores and other pore types (see: Zhao et al., 2015; Gao et al., 2016; Lai et al., 2017, 2018), which There are large differences in size, distribution and connectivity (see A. Sakhaee-Pour and Steven L. Bryant, 2014; Xiao Dianshi et al., 2017). The complex pore-throat network of tight reservoirs has a particularly significant impact on reservoir physical properties, especially permeability (see Zhao et al., 2015; Lai et al., 2016, 2018; Schmitt M et al., 2015), and its controlling effect It mainly depends on the development of movable pores in the pore system (see Xi et al., 2016; Huang et al., 2018). Generally, in high-permeability sandstones, the pore-throat radius is large enough to connect the pores with each other and the fluid mobility is strong (see Kassab et al., 2017), while the tight sandstone with a large number of micropores makes the porosity-permeability difference. The relationship is complicated (see Schmitt M et al., 2015; Lai et al., 2016; Kassab et al., 2017; Wu Hao et al., 2017), especially the micropores associated with clay have a small contribution to fluid flow (see Lai et al., 2016, 2018). Therefore, the development difference of different types of movable pores is an important factor leading to the complexity of pore connectivity and thus affecting the macroscopic physical properties of the reservoir (see Huang et al., 2018; Xi et al., 2016; Lai et al., 2018; Xiao et al., 2017). ), the fine characterization of movable pores is of great significance to the exploration and development of tight oil and gas.

Using high-pressure mercury injection technology, parameters such as pore-throat radius and permeability contribution value can be obtained. Characterizing the pore-throat connectivity of tight reservoirs by the pore-throat radius size parameter and permeability contribution value is the main method for pore-throat connectivity research today ( See Xi et al., 2016; Wu Hao et al., 2017; Xiao Dianshi et al., 2017; Yan Qiang et al., 2018; Liu Hanlin et al., 2018), but high-pressure mercury intrusion mainly characterizes the pore-throat size distribution, and cannot intuitively reflect different The ability of fluid to flow in pores large and small. Nuclear magnetic resonance technology is one of the important means to obtain the distribution of movable fluids (see Huang et al., 2018; Shi Jianchao et al., 2016). At present, the evaluation of the total pore mobility of tight reservoirs also relies on nuclear magnetic resonance technology ( See Lai et al., 2018). For example, Wu Hao et al. (2015), Li Min et al. (2018), Shi Jianchao et al. (2016), Dai Quanqi et al. (2016), Huang et al. (2018), Li et al. (2018), Wu Yuping et al. (2019) through NMR technology can obtain parameters such as movable fluid saturation and movable fluid porosity of tight reservoirs, and use the above parameters to evaluate the mobility of tight reservoirs, and to study the mobility and influencing factors of different types of reservoirs. The mobility of different types of pores has not been studied.

It can be seen from the above that the existing evaluation of pore mobility in tight sandstone reservoirs mostly relies on parameters such as movable fluid saturation and movable fluid porosity obtained by nuclear magnetic resonance technology. The characterization of the mobility of different types of pores in tight reservoirs affects the understanding of the development law of movable pores in tight reservoirs, and reduces the success rate of tight oil and gas exploration and development.

SUMMARY OF THE INVENTION

Aiming at the above-mentioned problems that the existing methods lack the characterization of different types of pore mobility in tight reservoirs, the present invention provides a method for classifying and evaluating pore mobility in tight sandstone reservoirs, which can realize the analysis of different types of tight sandstone reservoirs. The evaluation of pore mobility makes the evaluation of reservoir pore mobility more in line with the actual geological conditions, and the evaluation results are more accurate.

In order to achieve the above purpose, the present invention provides a method for classifying and evaluating pore mobility of tight sandstone reservoirs, the specific steps of which are as follows:

S1. Prepare the sample and perform NMR and high pressure mercury intrusion tests on the sample

Prepare a sample, perform nuclear magnetic resonance test and high-pressure mercury intrusion test on the sample in sequence, and obtain the saturated water nuclear magnetic curve, the bound water nuclear magnetic curve, the mercury injection saturation S _Hg and the mercury injection pressure P _c ;

S2. Divide intergranular pores and intragranular pores

Draw the mercury intrusion curve, Pittman curve and fractal curve according to the mercury injection saturation S _Hg and the mercury injection pressure P _c , according to the boundaries of the "plateau section" and "increasing section" of the mercury intrusion curve, the apex of the Pittman curve and the turning point of the fractal curve , determine the boundary between the intergranular pores and the intragranular pores, and divide the intergranular pores and the intragranular pores according to the boundary;

S3. Divide movable pores and immovable pores

According to the relationship between the saturated water NMR curve and the irreducible water NMR curve, combined with the boundaries between the intergranular pores and the intragranular pores, the intergranular pores are divided into movable macropores and isolated macropores, and the intragranular pores are divided into movable micropores and Immovable micropores;

S4. Calculate the content of different types of pores

The saturated water NMR curve, the irreducible water NMR curve and the abscissa envelope surface are divided into four regions: the movable macropore region, the isolated macropore region, the movable micropore region and the immovable micropore region. The area ratio of the total envelope surface can be used to obtain the proportions of movable macropores, isolated macropores, movable micropores and immovable micropores in the total pores.

Preferably, in step S1, the specific steps of preparing the sample are: selecting typical sandstone of the tight sandstone reservoir in the study area, preparing a standard core plug sample with a length of 3 cm and a diameter of 2.5 cm, and performing salt washing, oil washing and drying treatment Get a sample.

Preferably, in step S1, the specific steps of performing the nuclear magnetic resonance test are:

Put the sample into the high-pressure saturated water instrument, and inject the pre-configured formation aqueous solution after vacuuming until the sample is completely saturated, carry out saturated water NMR measurement, and obtain the saturated water NMR curve;

The samples were centrifuged to the bound water state and subjected to bound water NMR measurement to obtain the bound water NMR curve.

Preferably, in step S1, before the high-pressure mercury intrusion test is performed, and after the nuclear magnetic resonance test is completed, the sample is washed with salt and dried.

Preferably, in step S2, the method of drawing the mercury intrusion curve, the Pittman curve and the fractal curve according to the mercury injection saturation S _Hg and the mercury injection pressure P _c is: taking the mercury injection saturation S _Hg as the abscissa, and the mercury injection pressure P _c is the ordinate to draw the mercury intrusion curve, take the mercury injection saturation S _Hg as the abscissa, and use the ratio of the mercury injection saturation S _Hg to the mercury injection pressure Pc S _Hg /P _c as the ordinate to draw the Pittman curve, and take the mercury _injection as the ordinate. The logarithm lg (P _c ) of the pressure P _c is the abscissa, and the logarithm lg (S _Hg ) of the mercury saturation S _Hg is the ordinate to draw the fractal curve.

Preferably, the apex of the Pittman curve is the point at which S _Hg /P _c reaches the maximum value, and this point is defined as the Swanson parameter, the pore diameter corresponding to the Swanson parameter is called Rapex, and the Swanson parameter is the difference between the intergranular pores and the intragranular pores. Demarcation point.

Compared with the prior art, the advantages and positive effects of the present invention are:

The invention divides the intergranular and intragranular pores of the reservoir on the basis of the nuclear magnetic resonance test and the high-pressure mercury injection test of the tight sandstone reservoir sample, and further divides the movable pores and the non-movable pores of the intergranular pores, respectively. The movable pores and immovable pores of intragranular pores are calculated, and the proportion of different types of pores is calculated to realize the classification and evaluation of the mobility of different types of pores in tight sandstone reservoirs. It solves the deficiency of the existing technology that only relies on nuclear magnetic resonance technology to evaluate the total pore mobility of tight sandstone reservoirs, makes the evaluation of reservoir pore mobility more in line with the actual geological situation, and the evaluation results are more accurate. The understanding of the development law of movable pores in the reservoir is more accurate, which effectively improves the success rate of tight oil and gas exploration and development.

Description of drawings

Fig. 1 is the flow chart of the tight sandstone reservoir pore mobility classification and evaluation method of the present invention;

Fig. 2 is the mercury intrusion curve schematic diagram of the sample of Chang 7 section in Xin'anbian area according to the embodiment of the present invention;

Fig. 3 is the Pittman curve schematic diagram of the sample of Chang 7 section in Xin'anbian area according to the embodiment of the present invention;

Fig. 4 is the fractal curve schematic diagram of the sample of Chang 7 section in Xin'anbian area according to the embodiment of the present invention;

Figure 5 is a schematic diagram of the pores corresponding to the "platform section" in the mercury intrusion curve of the Chang 7 section in Xin'anbian area according to the embodiment of the present invention;

6 is a schematic diagram of the pores corresponding to the “incremental section” in the mercury intrusion curve of the Chang 7 section in the Xin'anbian area according to the embodiment of the present invention;

7 is a schematic diagram of the classification of different types of movable pores in the Chang 7 section of Xin'anbian area according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of calculation results of different types of pore contents in Chang 7 Member in Xin'anbian area according to an embodiment of the present invention.

Detailed ways

Hereinafter, the present invention will be specifically described through exemplary embodiments. It should be understood, however, that elements, structures and features of one embodiment may be beneficially combined in other embodiments without further recitation.

In the prior art, the evaluation of pore mobility of tight sandstone reservoirs depends on parameters such as movable fluid saturation and movable fluid porosity obtained by nuclear magnetic resonance technology. The characterization of different types of pore mobility in sandstone reservoirs affects the understanding of the development law of movable pores in tight sandstone reservoirs, and reduces the success rate of tight oil and gas exploration and development.

In order to evaluate the mobility of different types of pores in the above types of tight sandstone reservoirs, the present invention provides a classification and evaluation method for the mobility of pores in tight sandstone reservoirs, considering the types of intergranular and intragranular pores in tight sandstone reservoirs. , combining high-pressure mercury intrusion and nuclear magnetic resonance analysis to achieve the division and comparison of different types of pore mobility in tight sandstone reservoirs.

Referring to Figure 1, the specific steps are:

S1. Prepare the sample and perform NMR and high pressure mercury intrusion tests on the sample

Prepare a sample, conduct nuclear magnetic resonance test and high-pressure mercury intrusion test on the sample in turn, and obtain the saturated water NMR curve, the bound water NMR curve, the mercury injection saturation S _Hg and the mercury injection pressure P _c .

Specifically, the specific steps of sample preparation are: selecting typical sandstone of tight sandstone reservoirs in the study area, preparing a standard core plunger sample with a length of 3 cm and a diameter of 2.5 cm, and washing salt, oil and drying to obtain the sample. Since the residual salt crystals and crude oil in the original core sample fill the pores, the purpose of washing salt, washing oil and drying the standard core plunger sample is to prevent the pores in the core sample from being filled and affecting the impact of The effect of experimental measurement of nuclear magnetic resonance test and high pressure mercury intrusion test.

Specifically, the specific steps for carrying out the nuclear magnetic resonance test are:

Put the sample into the high-pressure saturated water instrument, and inject the pre-configured formation aqueous solution after vacuuming until the sample is completely saturated, carry out saturated water NMR measurement, and obtain the saturated water NMR curve;

The samples were centrifuged to the bound water state and subjected to bound water NMR measurement to obtain the bound water NMR curve.

S2. Divide intergranular pores and intragranular pores

Draw the mercury intrusion curve, Pittman curve and fractal curve according to the mercury injection saturation and mercury injection pressure, and determine the intergranular according to the boundaries of the "plateau segment" and "increasing segment" of the mercury injection curve, the apex of the Pittman curve and the turning point of the fractal curve. The boundary between pores and intragranular pores, according to the boundary, the intergranular pores and intragranular pores are divided.

Specifically, the mercury injection curve is drawn with the mercury injection saturation S _Hg as the abscissa and the mercury injection pressure P _c as the ordinate, and the mercury injection saturation S _Hg as the abscissa, with the mercury injection saturation S _Hg and the mercury injection pressure as the abscissa. The ratio of P _c S _Hg /P _c is the ordinate to draw a Pittman curve, the logarithm lg(P _c ) of the mercury injection pressure P _c is the abscissa, and the logarithm lg(S _Hg ) of the mercury injection saturation S _Hg is The ordinate draws a fractal curve.

Among them, the apex of the Pittman curve is the point where S _Hg /P _c reaches the maximum value, which is defined as the Swanson parameter, the pore diameter corresponding to the Swanson parameter is called Rapex, and the Swanson parameter is the boundary point between the intergranular pores and the intragranular pores.

S3. Divide movable pores and immovable pores

According to the relationship between the saturated water NMR curve and the irreducible water NMR curve, combined with the boundaries between the intergranular pores and the intragranular pores, the intergranular pores are divided into movable macropores and isolated macropores, and the intragranular pores are divided into movable micropores and Immovable micropores.

S4. Calculate the content of different types of pores

The saturated water NMR curve, the irreducible water NMR curve and the abscissa envelope surface are divided into four regions: the movable macropore region, the isolated macropore region, the movable micropore region and the immovable micropore region. The area ratio of the total envelope surface can be used to obtain the proportions of movable macropores, isolated macropores, movable micropores and immovable micropores in the total pores.

Specifically, in step S1, before the high-pressure mercury intrusion test is performed, and after the nuclear magnetic resonance test is completed, the sample is washed with salt and dried. In the NMR test, the sample is saturated with the formation aqueous solution. Due to the high salinity of the formation aqueous solution, there are pores in the sample that participate in the crystallization of salts. Before the high-pressure mercury intrusion test, the purpose of washing the sample and drying the sample is to avoid the sample. The inside of the pores is filled, which hinders the injection of mercury during the mercury intrusion test and affects the accuracy of the mercury intrusion test.

The above method of the present invention divides the intergranular and intragranular pores of the reservoir on the basis of nuclear magnetic resonance and high-pressure mercury intrusion test analysis of the tight sandstone reservoir samples, and further divides the movable pores of the intergranular pores and the intragranular pores respectively. By comparing with immovable pores, and calculating the proportion of different types of pores, the evaluation of the mobility of different types of pores in tight sandstone reservoirs is realized. It solves the deficiency of relying solely on nuclear magnetic resonance to evaluate the total pore mobility of tight sandstone reservoirs, makes the evaluation of reservoir pore mobility more in line with the actual geological conditions, the evaluation results are more accurate, and the success rate of exploration and development is effectively improved.

The above method of the present invention is described below by taking the classification and evaluation of pore mobility of tight sandstone reservoirs in the Chang 7 Member in Xin'anbian area of the Ordos Basin as an example.

S1. Prepare a sample, and perform nuclear magnetic resonance and high-pressure mercury intrusion testing on the sample.

The typical sandstone of Chang 7 tight sandstone reservoir in Xin'anbian area of the Ordos Basin was selected to prepare standard core plug samples with a length of 3 cm and a diameter of 2.5 cm, and the samples were obtained after salt washing, oil washing and drying treatment. NMR test and high pressure mercury intrusion test. During the NMR test, first put the sample into the high-pressure saturated water instrument, and then inject the pre-configured formation aqueous solution until the sample is completely saturated, carry out the saturated water NMR measurement, and obtain the saturated water NMR curve; the sample is centrifuged to the state of bound water and Carry out bound water NMR measurement to obtain bound water NMR curve. After the nuclear magnetic resonance test is completed, the sample is subjected to salt washing and drying treatment, and a high pressure mercury injection test is performed to obtain the mercury injection saturation S _Hg and the mercury injection pressure P _c .

S2. Divide intergranular pores and intragranular pores.

The mercury injection curve is drawn with the mercury injection saturation S _Hg as the abscissa and the mercury injection pressure P _c as the ordinate. See Figure 2. In Figure 2, A is the "increasing section" of the mercury injection curve, and B is the "increase section" of the mercury injection curve. Platform Segment".

Taking the mercury injection saturation S _Hg as the abscissa and the ratio S _Hg /P _c of the mercury injection saturation S _Hg to the mercury injection pressure P _c as the ordinate, draw the Pittman curve, see Figure 3, there is a vertex in the Pittman curve, That is, the point at which S _Hg /P _c reaches the maximum value is defined as the Swanson parameter, and the pore size corresponding to the Swanson parameter is called Rapex. In the figure, C represents the intragranular pores with poor connectivity, and D represents the intergranular with good connectivity. Pore, Swanson parameter (or Repex) is the boundary point between intragranular pores C and intergranular pores D.

The fractal curve is drawn with the logarithm lg(P _c ) of the mercury injection pressure P _c as the abscissa and the logarithm lg(S _Hg ) of the mercury injection saturation S _Hg as the ordinate. The fractal curve of the tight sandstone reservoir of Chang 7 Member in Xin'anbian area is characterized by two segments, as shown in Fig. 4, where the left segment corresponds to the large pore throat, and the right segment reflects the small pore throat. The vertices in the Pittman curve basically coincide.

The above cut-off points coincide with the boundaries of the "incremental segment" and "plateau segment" in the mercury intrusion curve. After analysis, it is considered that the "platform section" corresponds to the large pores and fine throats, which are intergranular pores. The "incremental segment" corresponds to the intragranular pores and is an approximate "tree-shaped network of pores" (see Figure 6).

According to the boundaries of the "plateau section" and "incremental section" of the mercury intrusion curve, the apex of the Pittman curve and the turning point of the fractal curve, the boundary between the intergranular pores and the intragranular pores is determined, and the intergranular pores and the intragranular pores are divided according to the boundary.

S3. According to the relationship between the saturated water NMR curve and the bound water NMR curve, combined with the boundary between the intergranular pores and the intragranular pores determined in step S2, the intergranular pores with good connectivity are divided into movable macropores and isolated macropores. Intragranular pores with poor connectivity are divided into movable micropores and immovable micropores. Figure 7 shows the classification of different types of movable pores in the Chang 7 tight sandstone reservoirs in Xin'anbian area.

S4. Divide the saturated water NMR curve, the irreducible water NMR curve and the abscissa envelope into four zones: the movable macropore area, the isolated macropore area, the movable micropore area, and the immovable micropore area, and calculate four areas respectively. The area ratio of the interval to the total envelope surface can be used to obtain the proportion of movable macropores, isolated macropores, movable micropores and immovable micropores in the total pores. Referring to Fig. 8, the calculation results show that the content of intergranular pores in the Chang 7 Member tight sandstone reservoir in Xin'anbian area accounts for 34%, and the intragranular pores account for 66%. In the intergranular pores, the content of movable macropores accounts for 22.4%, and 11.4% of the intergranular pores lose their movable ability; in the intragranular pores, the content of movable micropores only accounts for 12%, and the immovable micropores reach 54%. Therefore, the intragranular pores are also movable under certain dynamic conditions, but the mobility is low.

The above-mentioned embodiments are used to explain the present invention rather than limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims all fall into the protection scope of the present invention.

Claims (4)

1. A compact sandstone reservoir pore mobility classification and evaluation method is characterized by comprising the following specific steps:

s1, preparing a sample, and carrying out nuclear magnetic resonance and high-pressure mercury injection test on the sample

Preparing a sample, and sequentially carrying out nuclear magnetic resonance test and high-pressure mercury injection test on the sample to obtain a saturated water nuclear magnetic curve, a bound water nuclear magnetic curve and mercury injection saturation S _Hg And mercury feed pressure P _c ；

S2, dividing inter-particle pores and intra-particle pores

According to mercury saturation S _Hg And mercury feed pressure P _c Drawing a mercury intrusion curve, a Pittman curve and a fractal curve, determining the boundary of inter-granular pores and intra-granular pores according to the boundary of a 'platform section' and an 'increasing section' of the mercury intrusion curve, the vertex of the Pittman curve and the turning point of the fractal curve, and dividing the inter-granular pores and the intra-granular pores according to the boundary; according to mercury saturation S _Hg And mercury feed pressure P _c The method for drawing the mercury intrusion curve, the Pittman curve and the fractal curve comprises the following steps: at mercury ingress saturation S _Hg As abscissa, with mercury feed pressure P _c Drawing mercury injection curve for ordinate to obtain mercury saturation S _Hg As abscissa, in mercury saturation S _Hg With pressure P of mercury entering _c Ratio S of _Hg /P _c Plotting a Pittman curve for the ordinate to the mercury inlet pressure P _c Log of lg (P) _c ) As abscissa, in mercury saturation S _Hg Log lg (S) of _Hg ) Drawing a fractal curve for the ordinate; the vertex of the Pittman curve is S _Hg /P _c Defining the point reaching the maximum value as a Swanson parameter, wherein the pore diameter corresponding to the Swanson parameter is called as Rapex, and the Swanson parameter is a boundary point of the intergranular pores and the intragranular pores;

s3, dividing movable pores and immovable pores

According to the relation between the saturated water nuclear magnetic curve and the bound water nuclear magnetic curve, combining the limits of inter-granular pores and intra-granular pores, dividing the inter-granular pores into movable macropores and isolated macropores, and dividing the intra-granular pores into movable micropores and unmovable micropores;

s4, calculating the contents of different types of pores

Dividing the saturated water nuclear magnetic curve, the bound water nuclear magnetic curve and the abscissa enveloping surface into 4 regions of a movable macropore region, an isolated macropore region, a movable micropore region and an unmovable micropore region, and respectively calculating the area ratio of the four regions to the total enveloping surface to obtain the proportion of the movable macropore, the isolated macropore, the movable micropore and the unmovable micropore in the total pore.

2. The tight sandstone reservoir pore mobility classification and evaluation method of claim 1, wherein in step S1, the concrete steps of preparing the sample are as follows: selecting typical sandstone of a compact sandstone reservoir in a research area, preparing a standard core plunger sample with the length of 3cm and the diameter of 2.5cm, and performing salt washing, oil washing and drying treatment to obtain the sample.

3. The tight sandstone reservoir pore mobility classification and evaluation method of claim 1 or 2, wherein the step S1 of performing the nuclear magnetic resonance test comprises the following specific steps:

putting the sample into a high-pressure saturated water instrument, vacuumizing, injecting a pre-prepared stratum aqueous solution until the sample is completely saturated, and performing saturated water nuclear magnetism measurement to obtain a saturated water nuclear magnetism curve;

and (4) centrifuging the sample to a bound water state and carrying out bound water nuclear magnetic determination to obtain a bound water nuclear magnetic curve.

4. The method for classifying and evaluating the pore mobility of the tight sandstone reservoir of claim 3, wherein in the step S1, before the high-pressure mercury intrusion test is carried out, and after the nuclear magnetic resonance test is finished, the sample is subjected to salt washing and drying treatment.

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