RU2797175C1 - Method of well construction in complicated conditions - Google Patents

Abstract

FIELD: construction of oil and gas wells.

SUBSTANCE: invention relates to methods of opening local intersalt layers with abnormally high formation pressure and low reservoir properties. High-pressure local inter-salt interlayers are exposed by drilling on a biopolymer salt-saturated solution with an increase of the density of the drilling fluid when a gas-oil-water intrusion is detected. Drilling is continued to the planned depth using the drilling fluid with a density of 1750 kg/m³, conditional viscosity of 55 seconds and acidity parameter of 9.0-9.5, with a constant two-phase flow at the well outlet and gas flow into the block of receiving tanks with a degasser. Next, the casing string is lowered to the planned depth, flushing is performed to replace it with degassed drilling fluid, the casing string is cemented, and excess pressure is created for the period of waiting for the cement stone to harden.

EFFECT: increased efficiency of drilling wells with the possibility of continuing drilling to the underlying reservoirs of oil and gas without a significant increase in the time of well construction.

1 cl, 1 ex

Description

The invention relates to the construction of oil and gas wells, in particular, to methods for drilling local intersalt interlayers with an abnormally high reservoir pressure (AHRP) of the fluid system and low porosity and permeability properties (PRP) to continue trouble-free drilling to the underlying oil and gas reservoir.

A feature of the geological structure of hydrocarbon fields in Eastern Siberia are oil and gas saturated reservoirs with different reservoir properties and very different productivity indicators. So, there may be zones, the brine flow rate of which is more than 1000 m ³ /day, and the brine pressure reaches geostatic. There are also zones with low reservoir properties, the flow rate of which can be from 0.1-0.2 m ³ /hour for liquid and up to a thousand cubic meters per day for gas. The mineralization of brine can reach 600-630 g/l, while the salts of magnesium, potassium, calcium, lithium and other metals are found in high concentrations in the brine. In the process of interaction of magnesium salts with the drilling fluid, the water loss parameter begins to increase sharply, the volume in the receiving tanks also begins to increase, this indicates the inflow of brine or brine with gas into the well. At the same time, the formation pressure of the fluid in such low-permeability zones can also be close to geostatic, which significantly complicates the elimination of gas, oil and water intrusion in such wells. It is also obvious that it is the factor of high fluid pressure, which is gradually restored in the contact area of the bottomhole formation zone - casing string to the initial values in the formation, which plays the main role in the occurrence of collapse of the casing strings after their fastening.

The main difficulties in drilling wells are caused by gas saturation of the reservoir, because in the presence of AHFP, hydrocarbon gas from such a formation constantly flows into the wellbore, reduces the density of the drilling fluid, increasing the drawdown on the developing formation, which in turn increases the flow rate of the developing formation. It should be noted that, as a rule, such formations, even with gas saturation, are able to transfer the well from a static state to a slight overflow over a rather long period of time (from a day or more). This is due to the fact that at high fluid pressure, these formations have extremely low permeability values, which leads to an extremely low flow rate of formation fluid inflow into the well. Despite this, it is not possible to continue drilling due to the constant gassing of the drilling fluid, its foaming and the inability of the wellhead equipment to pump aerated drilling fluid.

Considering the high rates of development of engineering and technology in the last decade, the construction time for deep production and exploratory wells for oil, gas, industrial brines has significantly decreased from several months to 20-30 days (on average). The development of engineering and technology primarily concerns the use of top drives, telesystems with hydraulic and electromagnetic communication channels, rotary controlled systems, PDC bits of a very wide range of designs, etc. In turn, natural factors, such as the beginning, development of oil and gas shows in the well and methods for their elimination, as before, require long-term technological operations and, in the current conditions, significantly increase the time of well construction. And here it is very important to understand and evaluate the current geological section, its features, and most importantly, at least the approximate characteristics of possible developing layers in the well. These characteristics certainly include reservoir pressure and reservoir properties. It is from reservoir properties that, as a rule, depends the rate of reaction of the well to the emerging drawdown on the reservoir and, accordingly, the intensity of gas-oil-water intrusion. At the same time, if reservoir properties are low enough, the authors propose an alternative well-known method of drilling a well, which can significantly reduce time costs compared to standard methods for eliminating gas, oil and water intrusion.

A known method of ensuring the safety of drilling operations when opening high-pressure formations, consisting in the use of special weighted drilling fluids for the prevention of blowouts [Kalinin A.G., Levitsky A.Z. Technology of drilling exploratory wells for liquid and gaseous minerals. - M.: Nedra, 1988. - p. 98-99. Bulatov A.I., Penkov A.I., Proselkov Yu.M. Handbook of flushing wells. - M.: Nedra, 1984. - 317 p.]. Their preparation requires expensive and scarce reagents: bromides and nitrates of polyvalent metals, biopolysaccharides, hydroxyethylated derivatives of cellulose and polyhydric alcohols, barite, celestine, hematite, galena, etc.

The disadvantages of this method are the high cost of the drilling fluid, the great difficulty in its preparation and maintaining the required technological parameters (high rheological parameters) in the conditions of fluid flow from the AHFP formation. The main problem here is the formation pressure values close to the geostatic pressure values. With such a density (2300-2500 kg/m ³ ) drilling fluids behave extremely unstable, and often the required density is unattainable.

A known method for preventing annular gas-oil-water shows in oil and gas wells (RF patent for the invention No. 2493354, IPC E21V 33/13 (2006.01), C09K 8/48 (2006.01), issued on 09/20/2013), including filling the annular space above the cement mortar with clay mortar . According to the invention, a barite-weighted, unstabilized slurry is used, which is pumped during the cementing process before the cement slurry to create a barite plug, and the volume of the weighted slurry is not less than the volume of the annulus above the cement.

The disadvantage of this method is the large time costs for the physical deposition of weighting agents (barite, hematite, etc.), when storing the weighted solution in containers, partial sedimentation of the weighting agent may occur, which will lead to a deviation of the actual concentration of the weighting agent from the planned one. This method includes running an additional casing string after passing through the AHRP formation, which significantly increases the weight and cost of the well design.

A known method of isolating the inflows of strong brines (brine) in a well (USSR author's certificate No. 1444505, IPC E21V 33/13, issued 12/15/1988), including isolation of the inflows of brine due to the formation of a plug in the wellbore from sedimentation material and the crystallization of salts when the inflow is called from the well, at which the rate of the upward flow of brine will be less than the rate of settling of particles of sedimentary material.

The disadvantage of this method is the impossibility of further deepening the well, since after drilling the plug in the wellbore, the fluid inflow will resume.

A known method of creating a filtration screen when drilling high-pressure formations saturated with strong calcium chloride brines (RF patent for the invention No. subsequent precipitation of CaCO ₃ and reduced filtration from the formation.

The disadvantage of this method is the impossibility of pumping any active liquids (chemical buffers, quick-setting mixtures, cement) into the reservoir due to the low reservoir properties of such a reservoir, and hence the complete lack of injectivity. And when the hydraulic fracturing pressure values are reached during the injection process, the flow rate of the AHFP reservoir can only increase due to artificially improved reservoir properties in the bottomhole formation zone (BFZ), which will further aggravate the situation at the well.

There is a known method of opening a productive formation on depression (RF patent for the invention No. 2540701, IPC E21V 21/14, issued on February 10, 2015), which is essentially an adapted method of the previously known method (RF patent for the invention No. 2199646, IPC E21V 21/14, issued on February 27, 2003). Also, various sources mention the possibility of drilling with constant gassing of the drilling fluid, but only in accordance with the principles of drilling technology "on balance". in conditions of long-term developed deposits, compensation of pressure at the bottom by the operation of the throttle at the wellhead during various technological operations.

The main disadvantage of underbalanced and controlled pressure drilling (on balance) is the very high price of a set of equipment and the disproportionate increase in capital costs for well construction.

A known method of well construction in complicated conditions (RF Patent for the invention No. 2630519, IPC E21V 21/08 (2006.01), E21V 43/10 (2006.01), E21V 33/14 (2006.01), issued 09/11/2017), including drilling and fastening wellbore with a casing string to the roof of a high-pressure formation, opening by drilling high-pressure formations using anti-flow measures. After the opening of high-pressure formations, a sump of 30 m is drilled, and buffer fluid based on chilled brine is injected into the bottomhole formation zone.

The disadvantages of this method are its focus only on saturated high-pressure formations, and it is inefficient in case of gas shows in the well. Additional time and materials are also required to isolate the AHFP formations.

The closest in technical essence (prototype) is the method generally described in [Control of wells with GNVP. Practical tasks for well management: textbook / V.A. Dolgushin, A.A. Zemlyanoy, A.V. Kustyshev, D.S. Leontiev - Tyumen: Tyumen State Oil and Gas University, 2016. - S. 30-46], which consists in the fact that at the first signs of gas and oil and water shows (GOIP), namely the presence of a two-phase flow at the well outlet, long-term work is carried out to eliminate the GOP with weighting of the density of the drilling fluid above formation pressure gradient until a single-phase flow of drilling fluid is achieved at the inlet and outlet of the well.

The disadvantages of this method is that under the conditions of a local intersalt intersalt with a high pressure fluid system and low reservoir properties, it is necessary to weight the drilling fluid for a long time to a density of 2300 kg/m ³ and more with complete flushing of gas packs along the wellbore and achieve a single-phase flow of the drilling fluid at the exit from the well, weighting of the well structure for additional overlapping of inter-salt interlayers; Also, possible hydraulic fracturing of underlying and overlying rocks during drilling at a density of more than 2300 kg/m ³ can lead to geological complications and additional costs. At a density of 2300-2500 kg/m ³ drilling fluids behave extremely unstable, and often the required density of the fluids is unattainable.

The common disadvantages of all the above methods is the need for complete isolation of developing layers, which is always associated with long time costs. In the current conditions of high commercial well construction rates, long-term elimination of complications significantly reduces the technical and economic indicators of well drilling. Currently, it is required to develop ways to eliminate complications with minimal time.

The objective of the invention is to develop a method that ensures the continuation of trouble-free drilling to the underlying oil and gas reservoir in the conditions of exposed local intersalt layers with abnormally high formation pressure and low reservoir properties.

The essence of the invention is drilling through local inter-salt interlayers with abnormally high formation pressure and low reservoir properties without their isolation, with an increase in the density of the drilling fluid up to 1750 kg/m ³ , a decrease in the relative viscosity of the drilling fluid up to 55 seconds and a decrease in the acidity parameter of the drilling fluid pH to values 9.0-9.5 with constant degassing of the drilling mud at the wellhead.

The technical result is an increase in the efficiency of well drilling and the possibility of continuing drilling to the underlying oil and gas reservoirs without a significant increase in the time of well construction.

The technical result is achieved by the proposed method of well construction in complicated conditions, including drilling and fixing the wellbore with a casing string to the roof of a high-pressure formation with flushing with a single-phase drilling fluid, opening by drilling high-pressure local inter-salt interlayers using measures of blowout control on a biopolymer salt-saturated drilling fluid, weighting the density of the drilling fluid upon detection of gas, oil and ^water intrusion, while drilling is continued to the planned depth on a drilling fluid with a density of 1750 kg/m wells - drilling fluid and gas that enters the block of receiving tanks with a degasser for continuous degassing of the drilling fluid at the wellhead with gas separation into the atmosphere, then the casing string is lowered to the planned depth, then the well is flushed with an injection rate of the above drilling fluid of at least 15 l/s to replace the gassed drilling fluid in the annulus with degassed drilling fluid, then the casing string is cemented with cement slurry with a pumping rate of at least 15 l/s, after cementing, an excess pressure of 2-3 MPa is injected into the annulus for the waiting period hardening of the cement stone to reduce the likelihood of gas migration through the cement slurry at the time of its structuring.

Empirically, when drilling more than 15 wells, it has been established that an increase in density of more than 1750 kg/m ³ does not lead to a significant decrease in fluid production from a local intersalt intersalt with abnormally high formation pressure and low reservoir properties. At the same time, with an increase in the density of the drilling fluid more than 1750 kg/m ³ , the conditional viscosity increases significantly (and hence the static shear stress, dynamic shear stress, plastic viscosity, etc.). With an increase in the values of rheological parameters, the degassing of the drilling fluid is extremely difficult due to the fact that high values of internal friction of the drilling fluid significantly slow down the separation of gas from the drilling fluid and make it impossible to continue the process of circulation of the drilling fluid through the well due to the constantly decreasing density of the drilling fluid at the inlet into the well (due to its insufficient degassing after leaving the well). Reducing the conventional viscosity of the drilling fluid to values of 55 seconds is possible at the lower required pH values for the biopolymer drilling fluid. The pH range for the quality work of the biopolymer solution is between 9 and 10.5. Moreover, at lower pH values, the biopolymer does not work optimally, which in turn reduces the effect of the biopolymer on viscosity. Maintaining the pH values at the lower acceptable boundaries is facilitated by the flow of gas from the well. It has been experimentally established that with a constant flow of gas from the reservoir into the drilling fluid, a decrease in pH occurs due to its possible oxidation (the mechanism has not been fully studied). It has also been experimentally proven that a conditional viscosity of 55 seconds is sufficient to ensure that the weighting agent is kept in suspension in the drilling fluid.

At the same time, during long shutdowns (for example, for geophysical surveys of wells or tripping operations), the drilling fluid at the wellhead begins to "boil" 5-8 hours after the end of the last flush, that is, the drilling fluid in the well is evenly aerated with gas from a low-permeability formation. Such "boiling" of the solution can last for a day or more, but does not lead to a significant overflow from the well due to a very small gas flow rate from the low-permeability formation into the well and uniform gassing of the entire drilling fluid along the wellbore.

Traditional well drilling at depths over 1.5 km is carried out with a single-phase flow (liquid) at the inlet and outlet of the well. Traditionally, at the first signs of gas-oil-water shows (GOGWP), namely the presence of a two-phase flow at the well outlet, long-term work is carried out to eliminate the GOGWP until a single-phase flow of drilling mud is achieved at the inlet and outlet of the well. At the same time, the transition to drilling with a single-phase flow at the entrance to the well and a two-phase flow at the exit (liquid and natural gas) from the well, proposed by the authors in this method, allows continuing drilling without a significant increase in the cost of well construction, namely without weighting the drilling fluid to a density of 2300 kg/m ³ or more, weighting of the well structure for additional overlapping of inter-salt interlayers, possible hydraulic fracturing of underlying and overlying rocks when drilling at a density of more than 2300 kg/m ³ , which can lead to geological complications and additional costs

EXAMPLE

As an example, typical conditions are shown when drilling into local inter-salt interlayers with abnormally high reservoir pressure and low reservoir properties at one of the oil and gas condensate fields of the Lena-Tunguska oil and gas province (OGP).

The running depth of the previous casing string is 245 mm - 1100 m.

The depth of the high-pressure gas-saturated formation is 1600 m.

The pressure in the high-pressure gas-saturated formation is 37.9 MPa (formation pressure gradient 2.42 kg/cm ² per 10 m).

The flow rate of a low-permeability gas-saturated reservoir with high pressure gas flow rate is 350 m ³ /day at a drawdown of 12 MPa.

The flow rate of a low-permeability gas-saturated reservoir with high pressure gas flow rate is 550 m ³ /day with a drawdown of 18 MPa.

The density of the salt-saturated biopolymer drilling fluid at the time of opening the inter-salt formation was 1240 kg/m ³ .

Conditional drilling fluid viscosity - 55 seconds.

When drilling with a 215.9 mm bit at a drilling fluid density of 1240 kg/cm ³ with installed BOP equipment at the wellhead at a depth of 2150 m, a local intersalt interlayer with abnormally high formation pressure and low reservoir properties was exposed. When flushing the well, gas flow into the wellbore was recorded with an increase in gas readings up to 5-30% and a gradual decrease in the density of the drilling fluid to 800 kg/m ³ . The circulation of the drilling fluid was stopped due to the impossibility of degassing the drilling fluid at the wellhead to the initial values of the density of the drilling fluid. The density at the exit from the well is less than 800 kg/m ³ , the density after degassing is 1050-1100 kg/m ³ . At the same time, the density at the exit from the well continued to decrease. After the circulation is stopped, typical for intersalt interlayers with abnormally high reservoir pressure and low reservoir properties is the almost complete absence of overflow from the well (or a slight overflow of the aerated mixture up to 0.2-0.3 l/s) and the characteristic "boiling" of the drilling fluid at the wellhead. .

To solve this problem, the proposed method was used: drilling to the planned casing string depth with flushing with single-phase drilling fluid through local inter-salt interlayers with abnormally high formation pressure and low reservoir properties is carried out without their isolation, with an increase in the density of the biopolymer salt-saturated drilling fluid up to 1750 kg / m ³ (at the same time, the flow rate of gas flow into the well decreased with an increase in the density of the drilling fluid, which made it possible to conduct effective degassing of the drilling fluid at the wellhead without stopping circulation), reducing the conventional viscosity of the drilling fluid to 55 seconds (the fluid in the well was evenly saturated with gas, without forming large volumetric gas packs that can lead to a blowout from the well) and a decrease in the acidity parameter of the drilling fluid pH to values of 9.0-9.5 with a constant two-phase flow at the well outlet - drilling fluid and gas, and with the possibility of constant degassing of the drilling fluid at the wellhead with gas separation to the atmosphere. The drilling fluid was degassed into a block of tanks by using an intermediate settling tank and a permanently operating stationary degasser. Next, the casing string was lowered to the planned depth, then the well was flushed with an injection rate of at least 15 l/s to replace the gassed drilling fluid in the annulus, then the casing string was cemented with a cement slurry with an injection rate of at least 15 l/s, after cementing, an excess pressure of 2-3 MPa was injected into the annulus for the period of waiting for the cement stone to harden to reduce the likelihood of gas migration through the cement slurry at the time of its structuring.

At the same time, during long shutdowns (for example, for geophysical surveys of wells or tripping operations), the drilling fluid at the wellhead 5-8 hours after the end of the last flushing began to “boil”, that is, the drilling fluid in the well was evenly gassed with gas from a low-permeability formation. Such “boiling” of the mud could last for a day or more, but did not lead to a significant overflow from the well due to the very low gas flow rate from the low-permeability formation into the well and uniform gassing of the entire volume of the drilling mud along the wellbore.

Claims (1)

A method of well construction in complicated conditions, including drilling and fixing the wellbore with a casing string to the top of a high-pressure reservoir with flushing with a single-phase drilling fluid, opening by drilling high-pressure local inter-salt intersalts using measures of blowout control on a biopolymer salt-saturated drilling fluid, weighting the density of the drilling fluid upon detection of a gas-oil and water intrusion, characterized in that drilling is continued to the planned depth on a drilling fluid with a density of 1750 kg/m ³ , a conventional drilling fluid viscosity of 55 seconds and a drilling fluid acidity parameter of pH 9-9.5, with a constant two-phase flow at the well outlet - drilling fluid and gas that enters the block of receiving tanks with a degasser for continuous degassing of the drilling fluid at the wellhead with gas separation into the atmosphere, then the casing string is lowered to the planned depth, then the well is flushed with an injection rate of the above drilling fluid of at least 15 l / s for replacement of carbonated drilling fluid in the annulus with degassed drilling fluid, then the casing string is cemented with cement slurry with a pumping rate of at least 15 l/s, after cementing, an excess pressure of 2-3 MPa is created in the annulus for the period of waiting for the cement stone to harden to reduce the probability of gas migration through the cement slurry at the time of its structuring.