RU2109909C1 - Method for construction of wells - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this particularly relates to construction of wells in permafrost ground. Application of method ensures retaining integrity and tightness of production string in any conditions of freezing water-bearing media both in casing clearance and in annular space. Method implies locating in well casing pipes of various strength. Initially, proceeding from conditions of fail-safe construction of wells with respect to strength characteristics, selected is casing pipe which is nearest to production string. After that, preset is permissible external pressure of crushing production string. It must be higher than total pressure corresponding to ultimate breaking strength of casing pipe closest to production string and breaking pressure of frozen ground. Production string is selected according to aforesaid value. Strength characteristics of each subsequent casing pipe are preset proceeding from conditions of permissible pressure with respect to ultimate strength of internal casing pipe. EFFECT: higher efficiency. 1 dwg

Description

 The invention relates to the oil and gas industry and is intended for use in the construction of oil and gas wells in areas of permafrost.

 A known method of construction of wells, including the placement in the well of casing of various strengths [1].

 The disadvantages of this method are the low reliability of the structure in the conditions of propagation of permafrost and the associated possibility of crushing casing during freezing of aqueous media.

 A known method of well construction, including the placement of casing pipes of various strengths in a well [2], in which the strength characteristics of the casing pipes is selected from the conditions of the maximum possible pressures that occur when the liquid freezes, calculated according to the Clipperon-Clausius formula.

 The disadvantages of this method are that there is uncertainty when freezing water-containing media under the influence of atmospheric cold in winter, while there is no full guarantee that there will be no crushing or depressurization of the production string with increasing pressure. In addition, the strength characteristics of the support pipes are greatly overestimated, the metal consumption is increased, well construction is becoming more expensive due to the growth of capital costs.

 The challenge in creating the invention is the reliability and cost-effectiveness of well design at all stages, from construction, operation to completion of field development in conditions of permafrost propagation. The technical result, which the invention is directed to, is the preservation of the integrity and tightness of the production string under any conditions of freezing of water-containing media in both annular and annular spaces.

 The task and the technical result are achieved by the fact that in the known method of well construction, including the placement of casing pipes of various strengths in the well, in contrast to the prototype, first, from the conditions of trouble-free well construction, the casing pipe adjacent to the production string is selected according to the strength characteristics, then the permissible external pressure is set collapse of the production string, which should be greater than the sum of the pressure corresponding to the tensile strength adjacent to the operating casing casing string, and frozen fracture pressure, production casing is selected on it.

 The strength characteristics of each subsequent casing set from the conditions that the allowable pressure of the tensile strength of the inner casing is greater than the tensile strength of the outer casing.

The strength characteristics of the pipes correspond to the ratio
P _{see e.c.} > P _av . _Bl + P _rmp
P _pr.vn > P _{pr. Detection.} ,
where P _see.e.k is the crushing pressure of the casing of the production string;
P _av . _Bl - the pressure strength of the casing adjacent to the production casing;
P _rmp - pressure rupture of frozen rocks;
P _pr.vn - pressure strength of the inner casing;
P _pr.detection - pressure strength of the outer casing.

 Thus, we can conclude that the invention meets the criterion of "novelty."

 Since the use of the invention allows for the implementation of a long-existing need, the claimed invention meets the criterion of "inventive step".

 The drawing shows a diagram of the implementation of the method.

 Consider the implementation of the proposed method on the example of a three-column design of the well support used for the operation of the Cenomanian gas deposits of the Zapolyarnoye field.

 The external column (conductor) 1 is designed to overlap the upper weakly stable rocks.

 Intermediate (close to operational) column 2 is designed to prevent complications: gas phenomena, absorption of drilling mud, collapse of the walls of the wells, etc. The depth of its descent is determined both by overlapping the entire thickness of the frozen rocks, and by preventing gas breakthrough under the shoe during gas development and closed mouth. The column is used to install blowout equipment at the wellhead.

 Production casing 3 is lowered into the well and cemented after reaching the design depth and opening the productive horizon. Its integrity and tightness determines the life span of the well as a capital structure, its producing capacity, the ability to carry out various operations in the well: overhaul, stimulation of the flow, etc.

 Well construction begins with the choice of strength parameters of the intermediate string 2.

The diameter of the intermediate column is selected from the conditions:
1) the patency of the rock cutting tool (chisel) when drilling a wellbore under a subsequent string;
2) the creation of minimum hydraulic resistances in the annular space during cementing of casing strings to ensure a guaranteed rise of grouting mixtures to the design level.

 For our case, an intermediate column with a diameter of 299 mm, grade D steel, wall thickness 9.5 mm, external shear pressure 8.8 MPa, internal shear pressure 21.2 MPa, ultimate strength pressure 36.4 MPa.

After selecting the intermediate column 2, the determination of the strength parameters of the production column 3 from the condition
P _cm . ₃ > P _pr . ₂ + P _rmp
where P _{cm 3} is the crushing pressure of the production casing pipe 3, MPa;
P _pr.2 - pressure of the tensile strength of the casing 2 adjacent to the production string, MPa
P _{ex 2} = 36.4 MPa, P _rmp = 17.4 MPa;
P _cm . ₃ should be greater than 53.8 MPa.

 The diameter of the production casing is also selected based on the optimal thermodynamic working conditions of the elevator casing, which ensures the design production of formation fluid. That is, the development project sets the required internal diameter of the elevator pipes that ensure the project production.

 We select a real casing pipe with a diameter of 219 mm, steel grade “P”, with a wall thickness of 12.7 mm, the permissible external pressure for crushing of which is 54.0 MPa.

 The depth of descent of the production casing is determined by the depth of the lower perforation holes during the secondary opening of the productive object, taking into account the technological sump and the height of the cement glass in the casing.

H _e.k. = h _p + h _s + h _cs
where h _p - the depth of the lower holes of the perforation, m;
h _z - the height of the technological sump, m;
h _cs - the height of the cement glass in the column, m

 For deposits in the north of the Tyumen region, a conductor descent is a prerequisite, the purpose of which is to cover the entire thickness of frozen rocks, including the zero isotherm, which undergoes thawing both during well drilling and during its operation.

The selection of the strength characteristics of the conductor 1 is made from the condition
P _{ex 2} > P _{ex 1}
where P _pr.1 - the pressure of the tensile strength of the outer casing - conductor 1;
P _PR.2 - pressure ultimate strength of the intermediate inner casing 2.

 The tensile strength in the column is 2 pipes with a diameter of 299 mm, steel "D", the wall thickness of 9.5 mm - 36.4 MPa.

 As a conductor, a pipe with a diameter of 426 mm, steel "D", a wall thickness of 10 mm, and a tensile strength pressure of 26.9 MPa are selected.

 In wells constructed in areas of permafrost, during stops, reverse restoration of thawed frozen rocks occurs. When water-containing media freezes, the volume of the solid phase increases compared to the liquid, as a result of which significant pressures arise, leading to casing collapse.

 The proposed method provides the crushing of the casing outward, while maintaining the production string.

 The technical and economic efficiency of the method is to ensure trouble-free operation of the well for the entire planned period, the method does not limit the length of time the well is idle for repair and maintenance.

Claims (1)

A method of construction of wells, including placement of casing pipes of various strengths in the well, characterized in that first, from the conditions of failure-free construction of wells, the casing pipe adjacent to the production string is selected according to the strength characteristics, then the permissible external pressure of the production string collapse, which must be greater than the sum of the pressure, is set, corresponding to the tensile strength of the casing adjacent to the production casing and the fracture pressure of frozen rock; rayut production tubing, and strength characteristics of each subsequent casing is set a condition that the permissible internal pressure the tensile strength of the casing over the tensile strength of the outer casing which corresponds to the following relationships:
F _{with m. e . to} > R _{p p . b l} + R _{r m p}
P _{n on p. in n} > R _{p p . out.} ,
where P _{c m. e. k} - crushing pressure casing of production casing;
P _{n on p. b l} is the pressure of the tensile strength of the casing adjacent to the production casing;
P _{r m p} - pressure rupture of frozen rocks;
P _{n on p. in n} is the pressure of the tensile strength of the inner casing;
P _{n on p. n and p x y} - pressure limit of the outer casing strength.