RU2451786C1 - Method to construct deep wells under difficult geological conditions - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the field of drilling oil and gas vertical and inclined wells under difficult geological conditions. In the method for construction of deep wells under difficult mining and geological conditions with application of thin clay drilling muds of the following composition, wt %: clay 4.0-7.0, carboxymethyl-cellulose 0.5-2.0, sodium or potassium chloride 2.0-15.0, calcium carbonate 3.0-7.0, water - balance; or of the following composition, wt %: clay 4.0-7.0, carboxymethyl cellulose 1.0-3.0, sodium or potassium chloride 2.0-15.0, calcium carbonate 5.0-12.0, water - balance; drilling of geological elements that differ in complexity along a well length is carried out with one composition of a drilling mud, besides, tunnelling of filtering rocks is performed with account of preservation of natural permeability of productive reservoirs, elimination of inflows of a reservoir fluid into a well due to cooldown of a thin clay mud by 15-25°C with simultaneous increase of pressure in it by 3-6% from the mining one.

EFFECT: invention provides for stability of geological elements in tunnelling of wells, prevention of processes of drilling muds (fluids) absorption, inflows of a reservoir fluid, preservation of natural permeability of productive reservoirs by 80-90% from the initial values.

Description

The invention relates to the field of drilling oil and gas wells in difficult geological conditions.

In the construction of vertical and directional wells in difficult geological conditions, various methods are known for increasing the speed of rock drilling, for example, by increasing the pressure and temperature in the contact zone of the flushing fluid, which destroys the tool and the bottom of the well (K.V. Ioganson. Driller's satellite. Handbook. M., Nedra. 296 p.).

Known small clay drilling fluid containing clay, carbohydrate-simel cellulose (CMC) thermostable, starch, a reagent for regulating electrical resistivity, carbonate weighting agent and water (RF Patent No. 2323726, C09K 8/24, publ. June 27, 2008, analogue).

The use of this drilling fluid ensures well drilling in relatively stable rocks and conduct electrical logging studies by increasing the electrical resistivity at elevated temperatures. However, this composition of the solution cannot preserve the natural permeability of the reservoir of about 80-90%.

The closest to the claimed technical solution, taken as a prototype, is a method for controlling the fluid loss of a drilling fluid (RF Patent No. 2066684, C09K 7/02, publ. September 20, 1996), according to which the control of fluid loss is achieved by increasing the chloride salts in the solution along with CMC sodium or calcium. This method allows you to adjust the fluid loss from the drilling fluid, and in particular, to reduce it at the optimal costs of CMC and the viscosity of the fluid.

The tasks the invention is directed to are ensuring the stability of the walls of the wells, preventing the processes of absorption of drilling fluid and the influx of formation fluid into the well, as well as maintaining the natural permeability of the reservoir by 80-90% when drilling in difficult conditions of vertical and directional wells, this provides the possibility of sinking several horizons of different rock properties on the same chemical composition solution, while maintaining optimal sinking speeds and reducing costs at construction of deep wells in difficult geological conditions.

This is achieved by the fact that the drilling of geological elements of various complexity along the length of the well is carried out with one drilling fluid composition, and filtering rocks are drilled taking into account the natural permeability of productive reservoirs, eliminating formation fluid inflows into the well by cooling the clay solution at 15-25 ° C with a simultaneous increase in pressure by 3-6% of the mountain pressure.

The essential features of the proposed technical solution include the following:

- drilling of various geological elements of complexity along the length of the well is carried out by one composition of the drilling fluid;

- sinking of filtering rocks is performed taking into account the preservation of the natural permeability of productive reservoirs;

- inflows of formation fluid into the well are eliminated by cooling the clay solution at 15-25 ° C while increasing the pressure in it by 3-6% of the mountain pressure.

Signs that distinguish the claimed solution from the well-known developments were not identified in the study of this and related fields of science and technology, in other domestic and foreign sources. Thus, the claimed technical solution having the above set of essential features and advantages meets the criteria of patentability "novelty" and "inventive step".

The inventors in the laboratories of the Northern (Arctic) Federal University named after M.V. Lomonosov and during drilling at the Priobskoye field of wells using drilling fluids of different physicochemical properties obtained the following results.

Well construction in difficult conditions can be carried out on solutions that include, similarly to the prototype, the following reagents: bentonite clay (for structure formation, regulation of thixotropic properties, increase in retention and transporting ability of solutions); CMC, providing a decrease in filtration while stabilizing, regulating the rheological parameters of the drilling fluid; sodium chloride or potassium chloride (to reduce the lyophilicity of clays, inhibition of drilling fluid); calcium carbonate (chalk, marble chips, etc.), performing in the solution the functions of both a weighting agent and colmatant.

Studies have established that the speed of drilling in difficult conditions, along with the recommended composition of the prototype, the formulation of reagents for flushing fluids, is significantly affected by temperature and pressure, varying in a certain range of values: lowering the temperature by 15-25 ° C and increasing the pressure by 3- 6% of the mountain. According to research, with various complications in drilling, it is necessary to perform the following execution technology.

To ensure the stability of the walls of the wells, it is advisable to use a drilling fluid containing in wt.% The following reagents: clay - 4.0-7.0; CMC - 0.5-2.0; sodium chloride (potassium chloride) - 2.0-15.0; colmatant (calcium carbonate) - 3.0-7.0 and water.

Prevention of absorption of drilling fluids in permeable rocks is eliminated by using the following drilling fluid formulation, wt.%: Clay - 4.0-7.0; CMC - 1.0-3.0; sodium chloride (potassium chloride) - 2.0-15.0; colmatant (calcium carbonate - marble chips) - 5.0-12.0; water - the rest.

In the process of practical implementation of the method, a range of changes in temperature and pressure is determined. To prevent thermo-oxidative degradation of CMC, the washing liquid, as shown by studies, must be cooled by 15-25 ° C. It was found that cooling solutions by less than 15 ° C does not reduce the absorption of filtrates from them, and when the upper limit is reached, salts and colmatant are released from the cooled solutions.

To drill geological horizons of varying complexity in one solution, along with a slight adjustment of reagent concentrations and cooling the drilling fluid, it is necessary to increase the pressure in the solution by 3-6% of the rock, but not more than the values that lead to hydraulic fracturing of the rock formations. At the same time, studies have shown that increasing the pressure in the solution below the indicated values practically does not affect the absorption of flushing fluids into permeable rocks, and pressures above the recommended limit lead to a decrease in the permeability of productive reservoirs.

It was found that the exclusion of formation fluid inflows into the well, preservation of the natural permeability of productive reservoirs is ensured, for example, through the use of the following drilling fluid formulation, wt.%: Clay - 5.0; KMTS-500 - 2.0; sodium chloride - 15.0; colmatant - calcium carbonate (chalk) - 6.0; water - 72. In the process of drilling permeable rocks, the washing fluid (drilling fluid) is cooled by 20 ° C and the pressure in it is increased by 5% from the mountain pressure (ie, within the specified limits: temperature decrease by 15-25 ° C and increase pressure of 3-6% of the mountain).

The above composition and concentration of chemical reagents in solutions when working within the specified temperature and pressure limits allow unstable rocks to be drilled in the presence of acceptable values of water loss (5 ... 10 cm ³ ) and viscosity, providing the possibility of sinking several horizons of different rock properties on one chemical composition of the solution.

The above formulations of flushing fluids, the recommended limits of temperature and pressure changes in them together allow one to provide the possibility of sinking several horizons of rocks of different properties in the same chemical composition of the solution, to exclude the processes of loss of stability of the walls of the well, the absorption of flushing fluids into permeable rocks, formation fluid inflows into the well, maintain the permeability of productive horizons.

When comparing the above analogues and the prototype with the proposed method for the construction of deep wells in difficult geological conditions, the following technological differences were identified:

1) drilling of rocks of various properties is carried out on a solution of the same chemical composition;

2) for drilling complex geological horizons, the drilling fluid is cooled to 15-25 ° C;

3) when drilling wells in difficult geological conditions, the hydraulic pressure in the solution is increased by 3-6% of the mountain pressure.

Due to the implementation of fundamentally new technological operations, unlike analogues and prototype, it seems possible to reduce the cost of well construction in difficult geological conditions, increase hydrocarbon production from productive horizons and reduce the cost of resource supply of the process. The application of the technology proposed in practice will make it possible to reduce the costs of preparing flushing fluids, drilling deep wells by 5 ... 10% and ensure the safety of drilling operations in difficult mining conditions.

Claims (1)

A method of constructing deep wells in difficult geological conditions using low-clay drilling fluids of the composition, wt.%: Clay 4.0-7.0, carboxymethyl cellulose 0.5-2.0, sodium chloride or potassium 2.0-15.0 and calcium carbonate 3.0-7.0, the rest is water; or composition, wt.%: clay 4.0-7.0, carboxymethyl cellulose 1.0-3.0, sodium chloride or potassium 2.0-15.0, calcium carbonate 5.0-12.0, rest water; characterized in that the drilling of geological elements of varying complexity along the length of the well is carried out by one composition of the drilling fluid, and filtering rocks are drilled taking into account the preservation of the natural permeability of productive reservoirs, eliminating formation fluid inflows into the well by cooling the clay solution at 15-25 ° C with a simultaneous increase in pressure by 3-6% of the mountain pressure.