RU2066735C1 - Method for well casing in flow rocks - Google Patents

Abstract

FIELD: casing of oil and gas wells within the interval of rocks prone to plastic deformation. SUBSTANCE: method for well casing in flow rocks includes running of casing string with cementing collar into well. Cementing collar is lowered to the depth of flow rock bottom and cement slurry is injected into the casing string-borehole annulus below the bottom and roof of flow rocks. Nonsolidifying fluid is located in the interval of flow rock occurrence and is used in form of viscoelastic fluid with compressibility factor (β) determined by the condition

, where ΔV is change of volume of casing string-borehole annulus in casing string deformation, cu.m; V_o is initial volume of casing string-borehole annulus, cu.m; g is pressure in casing string-borehole annulus. Viscoelastic fluid is located by its injection into casing string-borehole annulus through cementing collar after cement slurry located above the roof of flow rocks. EFFECT: higher reliability in casing of well within the interval of flow rocks. 2 dwg

Description

 The invention relates to the field of fastening of oil and gas wells in the interval of occurrence of rocks, prone to significant plastic deformation.

 A known method of fastening wells in fluid rocks in the considered conditions, which consists in lowering the casing strings into the well and pumping cement into the annulus. Inside the column after cementing, a cement bridge is temporarily installed in the interval of occurrence of deforming rocks. The drilling of the bridge is carried out after covering the pipes with plastic rocks and creating uniform loading conditions (1).

 The disadvantage of this method is that it is not technologically advanced, because due to a possible error in calculating the time of removal of the cement bridge from the column.

 There is also a method of fastening wells in fluid rocks, including preparing a wellbore above the roof of fluid rocks and determining their flow rate. In the core of the flow, the rock overlaps the wellbore. After that, the casing is equipped with an end mill and a cutting element on the forming surface. Continuously rotating and unloading it with the circulation of flushing fluid, drill the core of fluid rocks. Cement the annulus above the sealed rock interval.

 This method is also unreliable, because can be used for fixing intervals of occurrence of potassium-magnesium salts with a high flow rate. In addition, the method is dangerous, because you have to use the casing as a drill string.

 The closest analogue of the invention is a method of fastening wells in fluid rocks, including lowering a casing string with a filling sleeve into the well, pumping cement into the annulus below the sole and above the roof of the fluid rock and placing non-hardening fluid in the annulus in the fluid bed (2) .

 The result is a cement ring having close contact with the rock and casing. An isolated section of the annulus in the interval of fluid bedding remains filled with drilling fluid, with the help of which the well was drilled.

 The considered technical solution assumes that the drilling fluid enclosed between cement plugs due to its low compressibility and tight isolation of the annulus will prevent direct casing contact with the mixing walls of the well, thus preserving a uniform, most favorable for the casing loading pattern for a long time.

 However, the implementation of this method will be hindered by the following circumstances.

 First, a cement stone that seals the annulus above and below the fluid bed is already permeable to water even at a pressure drop of 1.0 MPa.

 Secondly, the possibility of hydraulic fracturing of fluid rocks by liquid pressure in an isolated part of the annulus is not taken into account. All this reduces the reliability of the hermetic isolation of the cavity in fluid rocks, thereby reducing the reliability of the mounting of the well.

 The technical result of the invention is to increase the reliability of the fastening of the well in the range of fluid rocks.

где ΔV изменение объема затрубного пространства при деформации обсадной колонны, м³;
V₀ первоначальный объем затрубного пространства, м³;
g давление в затрубном пространстве, МПа,
при этом вязко-упругую жидкость размещают путем ее подачи в затрубное пространство через заливочную муфту после цементного раствора, размещаемого выше кровли текучих пород.The required technical result is achieved by the fact that in the method of fastening wells in fluid rocks, which includes running a casing string with a filling sleeve, injecting cement into the annulus below the sole and above the roof of the fluid rock, and placing non-hardening fluid in the annulus in the fluid bed , the filling sleeve is placed at the depth of the bottom of the fluid rock, and a viscoelastic fluid with a compressibility factor (β) determined from terms

where ΔV is the change in annulus volume during casing string deformation, m ³ ;
V _{0 the} initial volume of the annulus, m ³ ;
g pressure in the annulus, MPa,
in this case, a viscoelastic fluid is placed by feeding it into the annulus through the filling sleeve after the cement mortar placed above the roof of fluid rocks.

 A visco-elastic solution is placed over the reservoir to ensure tightness of the annulus and to prevent migration of the formation fluid through the annulus, especially when building gas wells containing aggressive components. A visco-elastic solution provides reliable isolation of annular space in the interval of occurrence of highly plastic rocks and thus provides the most favorable (uniform) casing immersion scheme.

 In FIG. 1 shows a general view of a well, where 1 denotes a fluid rock; 2 casing; 3 step cementing coupler; 4, 5 cement mortar; 6 viscoelastic solution.

 In FIG. 2 is a graph of the fracturing pressure P of rock salt versus viscosity T of various liquids, where curve 7 is for fluid rocks, curve 8 is for a visco-elastic solution.

 The method is as follows.

 In the well drilled in the deposits of fluid rock 1 (see Fig. 1), for example, potassium-magnesium salts, determine the depth of these rocks, the temperature of the reservoir and the pressure of salt rocks on the casing 2 in the interval of fluid rock 1.

 A casing 2 is lowered into the well, in which a step cementing sleeve 3 is installed at a depth of the bottom of the fluid rock.

 The first portion of the cement mortar 4 is pumped through the shoe of the casing 2 to cement the annulus below the bottom of the plastic rock. A second portion of cement mortar 5 is pumped through a step cementing sleeve 3 mounted in the base of the fluid rock to cement the annulus above the fluid rock roof.

 Sequentially after the second portion of the cement mortar, a visco-elastic mortar 6 is pumped through the sleeve 3. In this case, the zone of displacement of it with the drilling fluid behind the column formed in the first portion of the cement mortar during the injection of the second portion of the cement mortar through the coupling will be removed from the interval of fluid rocks through the wellhead and a visco-elastic mortar, with which a second portion of the cement mortar will be pressed, will be placed in the interval of occurrence of fluid rock between the first and second portions of the cement mortar.

где β коэффициент сжимаемости вязко-упругой жидкости;
DV изменение объема затрубного пространства при деформации обсадной колонны;
V₀ первоначальный объем затрубного пространства;
g давление в затрубном пространстве.The compressibility factor of a viscoelastic solution is selected from the following considerations. The compressibility of the fluid is associated with a change in the volume of the annulus during casing string deformation as

where β is the compressibility coefficient of a viscoelastic fluid;
DV change in annulus volume during casing deformation;
V _{0 is the} initial volume of the annulus;
g pressure in the annulus.

На основании соотношения (2) рассчитывают коэффициент сжимаемости β для конкретных размеров труб в реальных условиях в зависимости от определенных действующих усилий.From relation (1) we obtain the expression for β

On the basis of relation (2), the compressibility coefficient β is calculated for specific pipe sizes in real conditions, depending on certain acting forces.

При этом вязко-упругий раствор с данным коэффициентом сжимаемости подбирают экспериментально путем специальных лабораторных исследований по подбору жидкости, обладающей свойствами не фильтроваться через цементный камень и препятствовать гидроразрыву соляных пород, сохранив необходимые свойства прокачиваемости.Thus, to increase the casing string resistance, it is necessary to choose the compressibility coefficient of a viscoelastic fluid from the condition

At the same time, a viscoelastic solution with a given compressibility factor is selected experimentally by special laboratory tests to select a liquid that has the properties not to be filtered through cement stone and to prevent hydraulic fracturing of salt rocks, while maintaining the necessary pumpability properties.

 In addition, a necessary property of a viscoelastic solution should be its high stability. In FIG. Figure 2 shows the dependence of rock salt fracturing pressure on the viscosity of various liquids obtained as a result of research. Curve 7 shows this dependence for solutions such as saturated brines of sodium chloride, bischofite, and carboxymethyl cellulose (CMC) solution with different nominal viscosity, and curve 8 for a viscoelastic solution. This dependence shows that with an increase in the viscosity of a viscoelastic solution, which is a polymer composition, the fracture pressure increases linearly, while an increase in viscosity of a CMC solution does not give such an effect. It was also found that at a certain viscosity, the easily pumped polymer composition of the VUR is not filtered through cement stone with a sufficient pressure drop.

. Для перекрытия интервала пластичных пород спроектирована обсадная колонна диаметром 244,5 мм из стали Р110 с толщиной стенки 12 мм. Прочность этих труб на неравномерное давление составила P_кр 74 кг/см², т.е. значительно меньше, чем расчетное 210 кг/см².In a specific example, a potassium-magnesium salt formation was discovered in a well at a depth of 2203 2219 m with a formation temperature of 50 ^° C. The uneven pressure of salt rocks on the casing in this interval was calculated.

. To cover the interval of ductile rocks, a casing with a diameter of 244.5 mm from P110 steel with a wall thickness of 12 mm was designed. The strength of these pipes for uneven pressure was P _cr 74 kg / cm ² , i.e. significantly less than the estimated 210 kg / cm ² .

 However, when using the inventive technology, this casing will withstand geostatic pressure in the considered interval of rocks. This is due to the fact that the visco-elastic solution does not filter through the cement stone or through hydraulic fractures when compressing the well contour due to its low compressibility and sufficient viscosity, forming a sealed volume, the pressure of which gradually increases to the rock, which prevents the flow of rocks and eliminates their direct contact with the casing, and therefore eliminates the risk of uneven loading.

 Thus, the reliability of well fastening in the range of fluid rocks increases and the requirements for the strength parameters of casing strings are reduced in comparison with their calculation for uneven pressure.

Claims (1)

A method of securing wells in fluid rocks, including the descent into the well of a casing string with a filling sleeve, pumping cement into the annulus below the sole and above the roof of the fluid rock, and placing non-hardening fluid in the annulus in the fluid bed, characterized in that the filling sleeve is placed at the depth of the bottom of fluid rocks, and as a non-hardening fluid, a viscoelastic fluid with a compressibility factor / β / determined from the condition

where ΔV is the change in annulus volume during casing string deformation, m ³ ;
V _{0 the} initial volume of the annulus, m ³ ;
q pressure in the annulus, MPa,
in this case, a viscoelastic fluid is placed by feeding it into the annulus through the filling sleeve after the cement mortar placed above the roof of fluid rocks.

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