The Mechanism And Parameters-optimization Of Injection Fracture Pressure Propagation For Low Permeability Oil Field

Low-permeability reservoirs are rich in China. The low-permeability reservoirs account for a large proportion in the unused oil and gas geological reserves. At present, low permeability reservoir development is mainly depend on water flooding, but the special pore structure and water damage lead to difficult in injecting water, this reduce the sweep efficiency and recovery. There are two main ways which physical methods and chemical methods to enhanced water, mainly including conventional fracture, oscillation and acid etc to increase injection flow rate, but there are short valid, higher cost and secondary damage and so on.Fraction Propagation injection technology is proposed as a new measure which apply the principle of conventional hydraulic fracturing to increase injection water in low permeability reservoir, because the low permeability and high flow resistance, as well as the conventional into the impact of water quality, this lead to bad absorbing capacity. Under such circumstances, maintaining constant injection of water, improving the ground water pressure, when the stress reached the formation fracture pressure, there will be along the perpendicular to the direction of minimum principal stress fractures. Fracture surface were not contaminated, water-absorbent capacity enhance, and the ground injection water pressure will be instant down to in value. If the injection of water remains unchanged at this time. Pressure will be increase because of water on quality, sand production etc factors pollute the new sand surface of fractures during continue injection water process, a gradual increase in water stress, when the formation fracture pressure reached breakdown pressure, in the tip along the original fracture direction will generate a new fractures, new fractures surface permeability increased, water injection pressure reduce down instantly. And so on, fracture propagation appears an irregular cycle, fracture length increase until the scope of reasonable.In this paper, based on rock mechanics and fluid mechanics in porous medium,system study on fracture propagation mechanism. Firstly, the mechanism of fracture propagation mechanism is studied and developed mechanical model, building fracture propagation cycle, filtration coefficient and incremental long of fracture propagation Secondly, the fracture growth simulation and reservoir simulation is integrated to form a fracture propagation injection dynamic simulation software through two-way communication method, and the affecting factors of fracture propagation injection development is analyzed. Finally taking Sheng tuo Oilfield as example, parameters of fracture propagation injection technology are designed and optimized. Get the following conclusions:For low-permeability oil fields, it is remarkable for fracture propagation injection technology to enhance recovery , fracture affect the direction of fracture propagation effect :zero degree fracture recovery was slightly lower than the ideal state of degree of recovery, however recovery of forty-five degree and ninety degree fractures in according with the ideal state; and degree of reserve recovery of fracture propagation injection is much higher than conventional fracture sweep efficiency . sweep efficiency of zero degree fracture is the largest ,forty-five degree fracture take second place, ninety degree fracture less that , and without fracturing is the smallest at the ideal state.The effect of Injection volume on fracture propagation: the parameters used in the study, oil zero degree fracture is according with ideal state in recovery when the rate of injection of sixty square every day, injection volume of eighty square every day, the recovery of fractures compared with no fracture status is reduced; when injection volume of one hundred square every day, the recovery of decrease appear increased.The effects of water quality on fracture propagation: the effect of ninety degree and forty-five fracture propagation on recovery is negligible whether water quality is bad or good, fractures, recovery is high with the better quality when zero fracture but the affect is small. Water quality has little affected on the sweep efficiencyThe effects of well spacing on fracture propagation: the recovery is on the decline at any angle fractures in with well spacing increasing. The effects of well pattern on fracture propagation: fracture propagation injection is consistent with the ideal water injection with no fracture. That is, inverted nine spot flooding pattern slightly reduce the degree of recovery, other pattern is same. The effects of timing of water injection on fracture propagation: the earlier in the injection, the higher in recovery. However, the difference of ultimate recovery is not very great. No matter what circumstances, fracture injection technology can improve recovery at a large extent compared to taking into injection rate decline and have broad application prospects.