Study On The Physical Simulation Experimental With Hydraulic Fracturing Of Shale Gas Reservoir

Shale gas reservoir has low porosity and permeability characteristics, it also has the geological features that self-generating, self-storage and adsorption saturation. Shale gas which have hydrocarbon capability is enriched in shale layer in an adsorption or free state. For its larger flow resistance, shale gas with complex geological characteristics and low recovery ratio is difficult to product. Due to low permeability and markedly mechanical anisotropy in shale gas reservoir, horizontal wells fracturing technology is generally applied. Practice shows that horizontal wells combined with hydraulic fracturing technology has become an important technology to the development of low permeability reservoirs, especially to exploit dense shale reservoirs, which is a key technology to achieve its cost-effective exploitation. In our country, shale gas reservoir horizontal wells fracturing technology is still immature, and reservoir stimulation system has a lot of technical problems. This paper relays on the topic of" study on reconstruction technology of shale gas reservoir" to develop laboratory physics simulation experiment on hydraulic fracturing of shale gas reservoir horizontal wells. Firstly, this paper introduces the basic theory of horizontal well fracturing of shale gas reservoirs; Then design the laboratory experiment, including design principles of experimental, laboratory test system design of hydraulic fracturing and simulation model design; Finally, carry out the hydraulic fracturing test with the typical sample, analysis fracturing test results and time-pump pressure curve, and the different parameters effects on hydraulic fracturing and its fracture morphology. Experimental research findings can lay the foundation for the subsequent horizontal well fracturing simulation, and provide the experimental basis for the subject completion of the hydraulic fracturing process parameter optimization. Main contents and conclusions are as follows:1. The paper has discussed the occurrence mechanism and percolation mechanism of shale gas, physical models of fracture cracking, and fracture morphology and its extension criterion, which not only lay the foundation of laboratory hydraulic fracturing physical simulation experimental, but also provides a theoretical basis for the interpretation and analysis of the test results. Through the theoretical analysis, this method which physical simulation experimental can study on hydraulic fracturing of shale and the fracture morphology extended, and can systemic analyzes the different parameters effects on hydraulic fracturing.2. Based on research targets to carry on the laboratory experiment design. Firstly, study on servo control system of hydraulic fracturing equipment, acoustic wave test systems and sample preparation devices, and the laboratory hydraulic fracturing simulation test system have been established. Secondly, demonstrate the design principles of laboratory simulation experiment and its test method, experimental parameter design and simulation model design, and the steps and process of sample preparation in detail. Tests showed that the large manual simulation rock with300mm×300mm×300mm can ensure that the crack initiation and expansion have sufficient spatial dimensions, and setting different parameters, including various of perforation phase angle, segmented perforating and prefabricated cracks to study the effect of hydraulic fracturing test results.3. Laboratory physical simulation experiment of hydraulic fracturing was carried out according to the experiment design scheme. It includes of its operating steps, description and analysis of the experimental results. Through the typical rocks fracture morphology and its time-pump pressure curve after fracturing, fracture initiation of the change process, and the basic of extend proportionality can be interpreted. The experimental results showed that there are two cracks in the hydraulic fracturing process, the major fracture channel is due to shear failure inside of sample, the secondary fracture channel is owing to occurs tensile fracture internal of sample. The process of expansion and extension with hydraulic fracture all have followed failure criteria and fracture extension mechanisms.4. The laboratory experimental results indicated that two types of fracture morphology after fracturing include the regular and irregular surfaces. The basic rules of cracks extend is that the cracks along with the perforating direction firstly forms the initial crack, with increasing of pumping fracturing fluid, the sustained expanding of cracks. It cut-through the moment when it extends to a certain distance, so the fractures evolve into the flow channel of fracturing fluid. The formation mechanism of fracture channel which inside of sample break out shear failure, and fracturing fluid flows into the shear fracture plane to take place tensile failure, and prompted the crack tensile extension, resulting in cracks evolved into the fracturing fluid flow channel surface. For this test, the fracture parameters have a greater influence on the hydraulic fracturing experiment, the perforation angle is the main factor affecting the fracturing test and fracture morphology.In a word, through the hydraulic fracturing laboratory physical simulation experiment can initially explore the formation mechanism and propagation rule of hydraulic fracture cracks of shale reservoirs, as well as primary and secondary effects of different parameters on fracture morphology. The research results not only provide some experimental basis for the research team to achieve research objectives, but also provide technical support for the design of fracturing construction scheme.