RU2732161C1 - Method of construction of wells for prospecting and extraction of fluids accumulated in fracturing reservoirs - Google Patents

Abstract

FIELD: construction; mining.

SUBSTANCE: invention relates to the field of well construction, and in particular to the construction of the well associated with the natural fracture type reservoirs. Method involves primary opening of the reservoir with a well using a composite drill string. Well is drilled from the drilled cuttings by the ascending flow of drilling fluid. Production string is lowered and seams are separated in its annulus space and inflow of formation fluid is stimulated. At that, primary opening of the reservoir is performed with cleaning of the well from drilled rock - sludge with drilling fluid at reverse continuous flushing. Slime samples are taken to detect characteristic minerals for filling natural cracks and to determine intervals of natural fracture clusters from these data. Data on absorption of drilling fluid or inflow of formation fluids are used to cross clusters of natural cracks with open and closed mineralized fractures. Among clusters with open cracks data on intensity of absorption of drilling fluid or inflow of reservoir fluids during drilling are allocated clusters of cracks with industrial potential, which do not need stimulation at completion of well. Clusters with low potential are identified, which need stimulation of influx at well completion. Production string is equipped with devices separating clusters of natural cracks in aforesaid column space. Influx is stimulated in intervals of clusters of mineralized cracks and clusters of open cracks with low industrial potential. Performing perforation of production string in intervals of clusters of cracks, not requiring stimulation. Then the well is developed.

EFFECT: technical result is higher efficiency of construction due to prevention of colmatation of natural cracks and targeted stimulation.

1 cl, 3 dwg

Description

The technical field to which the invention relates

The invention relates to well construction processes. More specifically, it relates to well construction processes for the exploration and production of predominantly oil and gas. Even more specifically, it relates to the drilling and completion of wells for the exploration and exploitation of these resources associated with natural fractured reservoirs.

Examples of hydrocarbon accumulations in fractured reservoirs are deposits of the Bazhenov Formation in Western Siberia, ancient rocks of the Irkutsk amphitheater, the Bakken plei of North Dakota (USA), rocks of the crystalline basement of the White Tiger deposit in Vietnam.

Well construction for oil and gas exploration and production includes drilling, completion and well development.

Drilling a well involves creating a mine opening by breaking rock with a chisel. Completion of the well may include lowering the casing string overlapping the reservoir section of the well, isolating the formations in the annulus of this string, establishing a hydraulic connection between the inner space of the string and the reservoir, and taking measures to stimulate the inflow of in-situ fluid.

Well drilling involves the use of a drill string made up of separate pipes. As the hole deepens, the drill string length increases by adding separate drill pipes or plugs assembled from 2-3 drill pipes.

Opening of a hydrocarbon underground reservoir during drilling occurs using drilling fluids, often a suspension of clays in water or hydrocarbons.

Cuttings (cuttings) are carried to the surface by drilling fluid, usually delivered to the bottom of the well through the drill string. This type of well flush is known as direct circulation (direct flush). In direct circulation, the drilling fluid transports the cuttings to the surface through the annulus behind the drill string. The drilling fluid can be delivered to the bit and through the annulus behind the drill string. This type of wellbore flushing is known as reverse circulation (backflushing).

An important function of the drilling mud is to protect the reservoir from the harmful effects of the mud components. This function in granular reservoirs (for example, in sandstones) is realized by the formation of an impermeable mud cake on the borehole walls in the intervals of permeable rocks and by regulating the chemical composition of the drilling mud filtrate.

In fractured reservoirs, no mud cake is formed during drilling. Here the drilling fluid can enter the fractures traversed by the well. Through fractures with significant opening, cuttings can be transported by drilling mud at a considerable distance from the well. Drilling fluid, especially in high reservoir temperature conditions, can turn into “stone” in fractures, and a mixture of drilling mud and hard rock cuttings is “concrete”. Clogging of natural cracks occurs.

Fracture clogging occurs in both vertical and horizontal wells. As a result of clogging of cracks, the connection between the well and the reservoirs is either absent ("dry" well) or significantly hampered (low-productivity well).

To re-establish the connection between the well and the reservoir, costly work is being done to stimulate the formation fluid as part of the well completion.

State of the art

The problem of clogging of fractured reservoirs has been known for a long time. The industry has used a number of technologies to re-establish wellbore-reservoir connectivity and stimulate the flow of reservoir fluids.

We know a method of primary opening of a fractured reservoir under depression, the purpose of which is to prevent clogging of natural reservoirs. In accordance with this method, the drilling fluid pressure in the well is kept below the reservoir pressure. Formation fluid comes from the reservoir, excluding its clogging. This technology, the active application of which began in the late 1980s, is currently used to a limited extent, in particular due to the need to complicate the well design, the cumbersomeness of additional equipment, the reluctance of contractors to work with a "live" well due to the fear of an uncontrolled flow of hydrocarbons ( outdoor fountain).

Currently, the most widespread technology for well construction in fractured reservoirs is drilling a horizontal section in the reservoir and carrying out multi-stage multi-tonnage hydraulic fracturing (MMPF). It is precisely this technology that is used in the development of "shale" hydrocarbon deposits in the United States. The disadvantages of this technology include the lack of inflows of formation fluid for 50-60% of hydraulic fracturing stages. Those. $ 2-3 million spent on hydraulic fracturing at these stages are in vain. The reason for this situation is the practice of placing hydraulic fracturing stages evenly along the horizontal section due to the lack of geological criteria for the placement of hydraulic fracturing stages. With this arrangement, some of the stages are outside the zones of natural fracturing development, from where it is impossible to obtain an inflow.

The known method for the primary covering of a fractured reservoir in accordance with the patent of the Russian Federation 2602437, issued to Vakhrameev and others (prototype; hereinafter - "Method"). In accordance with the Method, after complete opening with the bit of each absorbing fractured interval, a clogging acid-soluble pack is placed in the interval of the absorption zone for temporary isolation of the absorption zone. Then, the bottom hole assembly is lifted and the drilling tool with the "funnel" is lowered into the absorption zone. After that, the colmatation pack is washed out. A certain volume of acid-resistant proppant is injected into the absorbing interval. The clogging acid-soluble pack is again placed in the open horizontal wellbore, overlapping the fractures filled with proppant. A round trip is performed to change the "funnel" to the bit. The initial drilling of the horizontal wellbore is continued until the next absorption zone. After that, the crack fixing operation is repeated. It is understood that after the well reaches the design depth, the mud packs will be removed by acid treatment.

The "method" has significant disadvantages. The isolation of intensive losses in fractured reservoirs, according to the experience of decades, including the use of various clogging materials, is often unattainable. The colmatation member appears in the crack. In addition, sequential, according to the Method, isolation of each lost circulation zone and proppant injection requires a large number of trips and trips of the drill string and a significant investment of time and money.

The objective of the present invention is to create a technology that improves the efficiency of construction of oil and gas wells confined to natural fractured reservoirs by preventing clogging of open natural fractures during initial drilling and by performing operations to stimulate the flow only in geologically favorable intervals, penetrated by the well.

Disclosure of invention

In the interval of the reservoir, the well is drilled with continuous reverse flushing, i.e. without stopping the mud pump during the extension of the drill string. Continuous backflushing eliminates the clogging of natural fractures with cuttings particles, the formation of cuttings plugs in the drill string, as well as mixing of cuttings from several intervals. The latter makes it possible to reliably tie in depth the rock samples obtained on the surface, i.e. to fix with sufficient accuracy the intervals of intersection of open and "healed" cracks by the well according to the appearance of specific minerals of filling the cracks (for example, calcite).

According to the intensity of losses of drilling fluid and occurrences of formation fluid, intervals of well intersection of fractures are determined, from which it is possible to obtain an industrial flow of fluids without stimulation (for example, hydraulic fracturing).

Fully or almost completely healed cracks are promising targets for stimulation, because at some distance from the well, these fractures can be open and hydraulic fractures can connect the well to such zones.

After reaching the final depth, a production string is run into the well. The production string is equipped with devices (for example, swellable packers) to isolate (separate) clusters of natural fractures.

The stimulation of the scheduled intervals is carried out. After that, the production string is perforated in the open fracture intervals, where no stimulation was required, and the well is completed.

The technical result of the invention is the elimination of clogging and the maximum preservation of the productivity of the most open natural fractures after the initial opening by drilling, as well as the determination of intervals of intersection by the well of clusters of mineralized fractures promising for stimulation, for example, hydraulic fractures.

Description of drawings

FIG. 1 shows the placement of equipment and the flow diagram of the drilling fluid when drilling a well with continuous backwash

FIG. 2 shows a diagram of the drilling fluid flow during backward continuous flushing at the time of preparation for extension of the drill string.

FIG. 3 shows a diagram of the reservoir section of the well, prepared for development after operations to stimulate the flow and perforation of the string.

Implementation of the invention

As shown in FIG. 1, well 2 penetrates the oil reservoir 1 from under the casing shoe 6. For drilling, a composite drill string 8 is used, which transfers rotation to the bit 10 from the top drive 12. The well is cleaned of cuttings (cuttings) with drilling mud 14 according to the backwash scheme. The drilling fluid is supplied by the pump 16 along the line 17 into the annular space between the casing 6 and the drill string 8 through the lateral retraction of the rotary seal housing 20. The drilling fluid moves along the annular space behind the drill string to the bit 10, picks up cuttings 11, gets inside through the flushing holes of the bit drill string and transports cuttings to the surface. Further, through line 13, the drilling fluid with cuttings is supplied to the cleaning system 22. From the cleaning system, the drilling fluid through line 23 enters the settler 24, from where it is taken by the pump 16.

To build up the drill string without stopping the removal of cuttings, a continuous flushing system is used, which consists of a number of continuous flushing valves (CSP) at the upper end of all plugs included in the drill string after switching to continuous flushing drilling. Description of the tools of the continuous flushing system, which can be used in the implementation of the present invention, published in the article "Continuous flushing system ..." in the September 2015 issue of the journal Drilling & Oil, pp. 35-38, authors Ropyanoy A.Yu., Skoblo V.Z ., Strazhgorodsky S.I.

The flow diagram of the drilling fluid at the moment of readiness for extension of the drill string without stopping the flushing is shown in FIG. 2. The bypass line 32 is connected by a connector 33 to the side port (not shown) of the KNP 30. By turning the rod, the KNP working body is transferred from the first position to the second. In the first position, the movement of the drilling fluid occurs along the axial channel in the direction of the upper drive, as shown in FIG. 1. In the second position, the axial bore is closed, drilling fluid from the drill string is directed through the bypass line 32 and to the mud cleaning system. Now the upper drive 12 can be disconnected from the KNP 30 of the drilled plug 9 and the next plug with the KNP can be included in the drill string. After attaching this plug, by turning the stem, the valve body returns to the first position (axial flow). The bypass line 32 is disconnected from the side port of the valve 30. The flow distribution returns to that shown in FIG. 1. Well deepening can be continued

As shown in FIG. 1, well 2 in reservoir 1 exposed clusters of natural fractures 3, 4 and 5, identified by the presence of calcite in the corresponding interval, a typical fracture filling mineral.

During the passage of fracture cluster 3, the loss of drilling fluid with a loss of 5% of the pump flow rate was noted. The absorption stopped after 20 meters of penetration.

During the passage of the klster cracks 4 there was no loss of drilling fluid.

When passing through the claster of cracks 5, the absorption of the drilling fluid was noted with a loss of 50% of the pump flow rate. Loss continued after cluster 5 was completely penetrated. With a pump capacity of 20 liters per second, the rate of mud loss was about 850 cubic meters per day. Based on the lost circulation data, indicating a high production potential of cluster 5, it was decided to stop further deepening of the well.

FIG. 3 shows well 2, which penetrated reservoir 1 after exiting the casing 6. Well 2 penetrated clusters of natural fractures 3,4 and 5. klast In well 2, a liner 41 was run, secured in a string 6 by a liner hanger 43. The liner 41 is equipped with separating devices, for example, swellable packers 44,45,46,47, isolating the intervals behind the liner where the well 2 intersects the fracture clusters 3,4,5. In accordance with the data on the absorption of drilling fluid during drilling, it was decided to carry out hydraulic fracturing in the intervals of fracture clusters 3 and 4 and to develop fractures in cluster 5 without stimulation. After activating the separating devices 44,45,46,47, the liner 41 was perforated in the interval of the cluster of mineralized fractures 4 and hydraulic fracturing was carried out through the holes of perforation 52, the cracks of which were fixed with proppant 54. Then the liner 41 was perforated in the interval of cluster 3 and hydraulic fracturing was carried out through the holes of perforation 51, the fractures of which are fixed with proppant 55. After that, the liner 41 is perforated with holes 53 in the interval of cluster 5. Thus, the well is prepared to trigger the inflow of formation fluids.

A person with average knowledge in the field of geology and well drilling understands that the described technology of well construction in natural fractured reservoirs for the exploration and development of oil and gas fields is applicable for the exploration and exploitation of thermal waters and steam and that the given example of implementation of the technology is illustrative and cannot mean limiting the use of technology to a certain number of groups (clusters) of natural fractures. Likewise, the application of the technology is not limited to fractured reservoirs, but is extended to mixed-type reservoirs, for example, porous-fractured and fractured-cavernous.

Claims (1)

A method of construction of wells for exploration and production of industrially useful fluids - oil, gas, steam and water, accumulated in natural fractured reservoirs, including primary opening of the reservoir with a well using a composite drill string, cleaning the well from cuttings with an ascending flow of drilling mud, running the production string and separation of layers in its annular space and stimulation of the inflow of formation fluid, characterized in that the initial opening of the reservoir is carried out with cleaning the well from cuttings - cuttings with drilling mud during continuous reverse flushing, sampling of cuttings is carried out to detect characteristic minerals of filling natural fractures and determine accordingly Clusters of natural fractures intersected by the well with open and closed - mineralized fractures, among the clusters with open fractures, based on the data on the intensity of losses of drilling fluid or inflow of formation fluids during drilling, distinguish clusters of fractures with industrial potential that do not need stimulation during well completion, and clusters with low potential, which need to stimulate inflow during well completion, run into the well a production casing equipped with devices separating clusters of natural fractures in the annulus, stimulating inflow in the intervals of clusters of mineralized fractures and clusters of open fractures with a low industrial potential, perforating the production casing in the intervals of clusters of fractures that do not need stimulation, and conducting well development ...

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