RU2640844C1 - Method for running casing string in horizontal long-distance wellbore - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method includes drilling a horizontal wellbore interval "drawdown", lowering the casing string. After the casing string has reached the depth of the production string shoe, the descent is stopped, an intermediate washing with drilling fluid is carried out with simultaneous controlled supply of nitrogen till the values of hydrostatic pressure are stabilised at the level of formation pressure values to form equilibrium in the "well-formation" system. Then under conditions of formed equilibrium, running of the casing string to the planned well bottom is continued.

EFFECT: increased efficiency of oil and gas deposits development in a complex cavernous-fractured carbonate oil-saturated formation.

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Description

The invention relates to the oil industry, and in particular to the construction technology of deep wells, in particular to the casing run (OC) in difficult geological conditions.

The main problem that arises when drilling horizontal shafts and then securing them by lowering the casing string into horizontal shafts of long length under conditions of a reservoir with abnormally low reservoir pressure are differential hooks that occur either during the descent of the casing string or during the procedure of its extension. The anomaly coefficient in wells with abnormally low reservoir pressure can reach 0.77. At the same time, the interval is drilled on drilling fluid with a density of 960 kg / m ³ .

There is a method for drilling and completion with programmable pressure and a programmable pressure gradient (RF Patent 2455453, CL ЕВВ 21/08, 2008). This method describes the possibility of combining drilling technology with repression and depression by applying a seal that separates two different pressure zones in the well. In the zone above compaction, repression (bottomhole pressure is greater than reservoir pressure), below compaction, depression (bottomhole pressure is less than reservoir pressure).

This method has a disadvantage associated with the impossibility of lowering the liner in conditions of its being in two different zones in the well - in depression and repression. The process of tripping in this method involves securing the wellbore by strengthening the bottom-hole zone of the formation by forming a filter cake on the walls of the well. The process of fixing the barrel in this case does not allow to equalize the pressure in the reservoir and in the well, in connection with this, the problem of differential sticking remains unresolved. Thus, the use of this method in a complex cavernous-fractured carbonate oil and gas saturated formation of a long horizontal well is technically impossible.

The closest is the method of opening the reservoir on the "depression" (RF Patent 2540701, CL ЕВВ 21/14, 2013 (prototype)), which is essentially an adapted method (RF Patent 2199646, CL ЕВВ 21/14, 2002). This method describes in detail the technical aspects of the application of the "depression" drilling technology, such as changing the reservoir pressure during the drilling of the well in the conditions of oil and gas deposits that have been developed for a long time, compensating for bottomhole pressure with the throttle at the wellhead during various technological operations. This method has a significant drawback associated with the impossibility of lowering the casing in a depression on the formation. Technically, it is not possible to lower the casing with a sealed wellhead. The elements of the rotary preventer are not designed to pass the casing string in a well sealing environment. Also, this method is extremely expensive, significantly reducing the economic performance of the drilling company.

These methods have another significant drawback, namely, in conditions of a formation with an abnormally low reservoir pressure, they do not allow an accidental descent of the casing string. This is due to the large difference (more than 4 MPa) between the current hydrostatic and reservoir pressure in the well. It is this pressure difference that creates the conditions conducive to the occurrence of differential sticking when lowering the casing. Thus, this problem is a systemic one, that is, it regularly arises on each new well in the horizontal wellbore interval. There is a likelihood of not bringing the well to the planned bottom, up to the complete liquidation of the well.

The objective of the claimed method is the development of an effective algorithm for lowering the casing string into long horizontal wells in difficult geological conditions associated with abnormally low reservoir pressures.

The technical result is the technological reliability of the development of oil and gas deposits.

The problem is solved by the proposed method in that the claimed method of lowering the casing in a horizontal wellbore, including drilling the interval of the horizontal wellbore in the "depression", lowering the casing, characterized in that when lowering the casing into the horizontal interval after reaching the depth of the shoe the descent columns are stopped, an intermediate flushing with a drilling fluid is carried out with a controlled nitrogen supply until the hydrostatic values are stabilized pressure at the level of reservoir pressure values, while forming equilibrium in the "well-formation" system, then, under the conditions of the formed equilibrium in the horizontal bore interval, the casing continues to descent to the planned bottom hole.

In the event of a differential sticking, intermediate flushing is also carried out when the casing is lowered with drilling fluid with a controlled supply of nitrogen until the hydrostatic pressure is stabilized at the level of reservoir pressure in order to cause circulation in the wells with complete absorption of the flushing fluid.

The essence of the invention: maintaining the value of the bottomhole pressure in the well when lowering the casing string equal to the reservoir pressure. In the event that development begins, the well drowns out "itself" due to the flow of oil into the wellbore. The density of oil is greater than the reservoir pressure gradient.

EXAMPLE

(Based on geological and technical data for one of the deposits in the Republic of Yakutia.)

Consider the geological conditions and the permissible technological ranges for the selected conditions (Botuobinsky sandstone with anomalously low reservoir pressure (ANPD)).

Well depth 3900 m.

Depth of descent of the production casing OK 178-3150 m.

The anomaly coefficient in wells with ANPD can reach 0.77. At the same time, the interval is drilled on a drilling fluid of 0.96 g / cm ³ (960 kg / m ³ ).

The OK-114 shank is lowered to the shoe of the OK 178 production casing. Next, in the OK 178 shoe, intermediate washing is performed at a depth of 3150 m. At the same time, a controlled nitrogen supply is performed until the hydrostatic pressure drops below the reservoir pressure. After the entire well is filled with aerated fluid with a density of 0.77 kg / cm ³ , the OK 114 liner is lowered to the bottom.

Claims (1)

The method of lowering the casing string in a horizontal wellbore of long length, including drilling the horizontal wellbore interval in a “depression”, lowering the casing string, characterized in that when lowering the casing string into the horizontal wellbore interval after reaching the depth of the shoe of the production string, the run is stopped, intermediate drilling is carried out by drilling solution with simultaneous controlled supply of nitrogen to stabilize the hydrostatic pressure values at the level of reservoir pressure values, form yn thus balance the system «well - layer", hereinafter equilibrium conditions generated in the range of horizontal wellbore casing descent continues until the plan face.