Shale Gas Horizontal Well Fracturing Technology - Baidu Content
2017-05-25 12:01
The shale layer can be used as the source rock and reservoir rock of the gas. The reservoir has the characteristics of continuous distribution, low porosity, low permeability and high brittleness. The natural gas in the shale exists in three forms: the free gas in the rock's pores, the free gas in the natural cracks, and the adsorption of the organic matter on the surface of the mineral. These different reservoir mechanisms directly affect the way in which the shale gas develops, effectiveness.
Global energy research estimates that large shale gas resources are mainly distributed in North America, Latin America and the Asia-Pacific region. The study shows that the shale gas resources in the United States are about 415 000 × 10 ^ 520 000 ± 108 V and Canada is about 140 000 × 10 ^ 170 000 × 10 ^ ^ 3, and the shale gas recoverable resources in China's major basins and regions are about 260 000 ° 108 V, while the study of resource conditions in other regions is very limited.
Experience in the development of shale gas in the United States shows that increased production technology, especially horizontal well fracturing, is critical to the development of shale gas. Other important technologies include horizontal well directional well drilling and reservoir description technology.
Shale gas completion
The Barnett Shale is the first shale gas that has been successfully developed in the United States and is currently the most prolific shale gas field in the United States and has become a model for the development of other shale gas fields in the United States and around the world. Barnett Shale development early use of straight well development, but the production effect is not ideal, before and after 2000, turned to horizontal wells development, yield 3-5 times to enhance. At present, the United States shale gas [1] almost all wells using horizontal wells, the depth is usually between 1 200 ~ 2500 meters, and the use of long radius of curvature <10. ~ 15730 0> made oblique, easy to post-measures measures. Usually the horizontal section length between 600 ~ 1 500 0, with the horizontal wells operating technology advances, the latest horizontal segment length of more than 3000. The majority of the 83 ° 611 shale wells have a higher level of 15 ^ 450> than the heel, which facilitates the return of the water to the lowest heel.
Horizontal well completions have undergone a transition from casing completion to openhole completion, see Figure 1. Early horizontal wells are usually 114.3 00 (bucket 1 //> or 139.7 00 "1 //> casing completions, fracturing with drillable bridge plugs to achieve multi-level fracturing .In 2012 more inclined to use the naked eye horizontal wells Multi-level fracturing method completed and put into production, fracturing series is gradually from 5 to 7, increased to 20. Barnite shale gas reservoir in the development of horizontal wells have tried the following several completion methods.
1.1 casing ten non-cementing ten perforation ten cage system fracturing
The typical completion of the Barnett shale is the use of a non-cementing liner in the horizontal section, which does not use mechanical steering at the time of fracturing, firing only a specific number of holes in the horizontal section casing and during construction Using large displacement <25-32 ^ 3 / ^ ^ ^) to obtain the current limiting effect. Part of the operation also used to block the ball and rock salt to help the flow of fluid between the blasthole. However, since the fluid can move freely in the casing and the naked eye ring space, cracks may be generated in any part of the horizontal section. Field microseismic monitoring also shows that fracturing fluid sometimes occurs in the casing, but cracks are generated and propagated completely random and are not necessarily in the casing perforation position, at any point in the wellbore, May happen.
1.2 casing ten cementing ten perforation ten flow limiting fracturing
The first use of cemented casing in the Barnett Shale is to apply fractal fracturing to improve the distribution of cracks in the entire well of the horizontal well. Current limiting technology mainly uses high displacement and blocking the ball 丨 rock salt to divert. Monitoring of these wells also shows that the propagation of fractures is very random and that cracks are almost unpredictable. The early comparison of the results of the above two completion modes shows that although cementing cement can play a certain degree of steering between the casing and the formation, it is usually open (not required) Higher than casing cementing completion.
1.3 casing ten cementing more than 10 fracturing
This is the most common form of shale formation (see Figure ^). When the well completes, the cement is injected into the casing in the horizontal wellbore, and then the multi-stage fracturing transformation of the "bridge plug ten hole" is carried out, that is, the mechanical seal in the casing is realized by means of cable or coiled tubing, To achieve the mechanical turn of the ring. Followed by repeated this process, in the horizontal section to complete multi-level fracturing transformation. When all the segments are processed, the composite tubing is used to drill down the composite bridge to reconnect the horizontal wellbore from the heel to the end. Although this approach can be achieved in the horizontal segment of the sub-steering transformation, but each level should use coiled tubing, perforating guns and fracturing equipment to operate, the production cost is very high, and operating efficiency is low and time-consuming. Studies have shown that the yield obtained by this approach is equally undesirable because cementitious cement blocks many natural fractures and joints, which are important for improving gas production.
1.4 Naked tenteen liner fractures
In 2006, a new type of open-hole multi-stage fracturing (1) fertilizer was completed in Texas 06 plus 0 ^ counties (see Figure)), which was originally proposed in 2001 to raise Multi-level fracturing time efficiency, reduce operating costs, improve system reliability and repeatability. Naked multidimensional fracturing system is used to isolate the layers by means of a hydrostatic septum packer instead of cement cementing. The packer usually uses an elastic element to seal the openhole well without the need for lifting or drilling, The sleeve tool forms a channel on the wellbore between the packers to replace the perforation of the cannula. These skid tools can be opened by hydraulic or by pushing (with a number of> size-specific start-up balls to switch the sleeve and open the channels. These balls can be enclosed in two stages, eliminating the need for bridgeheads. The main advantage of the fracturing system is that all fracturing treatments can be completed in a row, without the use of bridge plugs, which saves time and costs. After the completion of the production operations, it can be quickly returned and put into production. Seat, to further increase production [1].
Foreign comparison of the Barnite shale cementing and naked eye multi-stage fracturing completion of long-term production results. The results show that although the casing is well occupied by some casing in the mainstream, the production effect of the Barnett Shale Openhole is obviously better than that of the cementing production. 031X611 ^ 0 ^ 06 ^ 61 and so on in 2010 compared to the two horizontal wells of Barnett parallel to each other wells, two wells using different completion methods: well people with naked eye multi-level completion (naked ten ten sets of 10 sets of ball fractures> The completion of the two well wells, the proppant and the amount of fracturing fluid are also close; however, during the three years of production, the cumulative production of the well is almost well 8 Of 2.5 times ⑸.
Recently, 03 ^ 611 et al. Also simulated the production failure profiles of the six-stage naked eye and the 6-stage casing well completion. The results show that the naked eye completions can better achieve the full level of the oil Horizontal section of the cement cementing hindered the production of the annulus; shale gas storage is usually natural cracks and joint development, naked eye completion Yi Yi can greatly play these natural cracks on the contribution of production.
Shale gas hydraulic fracturing
Shale belongs to an ultra-low permeability reservoir with a permeability of more than 0.00. 0.01 ^ 0, and therefore belongs to the "nano-Darcy" permeability formation, all reservoirs must be fractured before they can be put into production. Often the United States shale gas fracturing single well costs more than 5 million US dollars, is the horizontal well drilling costs 2 times. Shale gas wells using large-scale hydraulic fracturing, usually add 45 ~ 4501 proppant, fracturing fluid is usually 10,000- or more. In 2000, began to large-scale use of water fracturing, also known as drag reduction fracturing, than the cost of fracturing less liquid, and yield better. Many operators see water fractures as the most important revolution in the history of shale gas technology development.
2.1 fracturing fluid
Three kinds of liquid systems are mainly used in the shale gas fracturing of the United States: direct injection of liquid nitrogen, nitrogen bubbling and drag reduction. In addition to the cost advantage, the damping water can pump a large amount of water and a small amount of proppant under high displacement, and can carry proppant into a deeper fracture network, resulting in a larger crack network and a deflated area. Become a standard practice for fracturing operations.
Reduce the water composition of the water accounted for the vast majority of [99.5 ^>, it is also known as water fracturing, see Figure 2. Among the many additives, two kinds of agents which must be added are depressurizers and fungicides. The most commonly used antihypertensive agents are partially hydrolyzed acrylamides. Polyacrylamide is usually used with a built-in phase transfer agent or an additional phase transfer agent [reversible emulsion or hydrated polymer> used as an oil phase emulsion, while providing a certain viscosity and reduced friction. In order to improve the drag reduction effect, industrial anti-lowering agent products have a high molecular weight, for example, polyacrylamide and acrylic polymerization to form a polymer electrolyte, thereby increasing its drag reduction rate. Since the proppant delivery does not require high viscosity under fracturing turbulence conditions, it is possible to produce diversion fractures as long as the crosslinking liquid or the foam liquid at a lower cost.
2.2 proppant
For low shear water fracturing fluids, small diameter [40/70 mesh] proppants are commonly used, and smaller shale (100 mesh> proppants are required for shale formations developed for natural fractures). This is because in the drag reduction of water in the proppant of poor transmission performance, the use of small diameter will improve the suspension performance to a certain extent, but also can get a higher conductivity. There will be a large part of the cracks will not be supported, but due to shale rock brittle fracture, stratigraphic slip and proppant bridge block 丨 embedded effect, the fracture system will still form "infinite" diversion area, which Is the foreign scholars put forward the "no support" crack diversion capacity.
In the early reduction of water fracturing, some shale gas wells do not achieve sand fracturing also get a good production effect, so whether the need to support the fracturing proppant, the industry is still controversial, but more common understanding Yes, sand can improve the formation of diversion capacity, help to improve the yield effect.
2.3 fracturing process
Usually shale gas reservoirs are very thick, and shale development in the horizontal section of the length of the gradual increase in hydraulic fracturing construction in the horizontal section of the multi-level 7
, Each time the pump injection for the shale gas reservoir of a layer, every two paragraphs are separated. In addition, each layer of fracturing fluid in pumping will be divided into multiple slugs to complete, to form a more complex formation within the cracks network.
After the ground equipment test pressure, the first pump into a "rock acid" (usually only mouth) to clean the near well pollution; the second step is to inject "drag the water" slug, due to the addition of Jiang Zuji, water With a large displacement quickly into the formation; then, began to inject a large number of drag reduction water and low concentration of fine sand, during which gradually increase the concentration of sand; sand is about to end into the drag water and coarse sand, in order to maintain near the well cracks Open and get near the well high conductivity capacity; the final use of drag water washing wells back to clear the equipment and wells within the sand. After washing, the downhole tool is moved to another section to start the next level of fracturing construction.
In order to further improve the efficiency of operations and reduce operating costs, foreign recently in the shale gas development in the proposed "well plant" concept, the well site or platform as a joint operation of the "factory" will be drilling, cementing, perforation , Multi-level fracturing and other construction as a pipeline operation on a process, in the same well to complete the drilling wells, well completion and production. It has been reported that foreign countries have achieved a 16-well horizontal well in a well site, with a total of 400 fracturing completions. This mode of operation not only greatly improves the utilization of equipment and vehicle groups, but also makes the underground generated cracks network more complex, field applications also show that the production effect than the single well fracturing yield 75 ^ ~ 130 know 6 :.
In the fracturing, microseismic imaging and digital simulator can be used to monitor the crack characteristics in each class of shale reservoirs, observe the growth trajectories of fractures, and evaluate the height, length and orientation of fractures. In construction, the operator should pay particular attention to the vertical growth of the cracks to ensure that the hydraulic fractures do not penetrate the shale reservoir and extend to the adjacent water layer.
in conclusion
(1) horizontal well drilling and fracturing technology has become the mainstream of shale gas development technology.
Shale gas horizontal well fracturing completion of the application is more cementing perforation bridge plug fractures and naked multi-stage sliding sleeve fracturing, the latter can handle more than 20 times, improve the operating efficiency, and long-term production effect good.
(2) Reducing water fracturing can improve the complexity of cracks in shale reservoirs, reduce the cost and improve the yield and become the preferred liquid system for shale gas fracturing.
In the case of small diameter proppant, a large part of the cracks will be supported. However, due to the brittleness of the shale, the slippage of the rock and the bridging effect of the proppant bridge, the fracture system remains Will provide a higher "no support" crack diversion capability.
China's shale gas development is currently in its infancy and should integrate existing technology to strengthen research and focus on key technologies such as downhole tools, construction fluids and construction technology related to multi-level fracturing technology in open shale gas development. , To promote and achieve shale gas this "very gas" to "conventional gas" change.
