Adaptability Research Of Hybrid-fracs In The Fith Member Formation Of Xujiahe Formation In Xinchang Area

The fifth member formation of Xujiahe formation in Xinchang area, located in Xiaoquan the middle of west Sichuan depression. The west part of the large rumble strip in the east of Fenggu north east, is shallow lake plain and delta front sediments, the buried depth of foemation is 2500-3500 m and average thickness is 500.6m, which can be divided into upper, middle and lower three sub-segments, with 11 sets of sand bodies. The upper and lower sub-segments treat the sand-mudstone interbedded deposition as its major part, middle sub-segments treat the shale deposits as its major part. It required the mud and layer of the formation upper, middle and lower sub segments are 0.625、0.768 and 0.55 respectively. The favorable district of the main layer in this gas reservoir, reserves 7.85×1010m3, which has great potential for development. Because the poor physical properties and low porosity and permeability of the gas reservoir, it is difficult to rely on the natural productivity for industrial mining. According to domestic and international experience in exploiting unconventional gas development, the use of large-scale friction-reduced fracturing fluid, can obtain a large stimulated reservoir volume which is an effective technique to achieve such gas reservoir development. However, the interbedding and the fifth member formation sand and shale have complex characteristics, friction-reduced fracturing fluid fracturing will form large area of noneffective fracture easily, resulting in low production of fractured wells and having a short time of stable production. After investigation, we use the collaboration of friction-reduced fluid, linear gel or cross linked gel and other liquid to fracturing which can compensate for deficiencies of friction-reduced fracturing fluid. While obtaining large stimulated reservoir volume, we can improve proppant volume by cross linked liquid and achieve effective support for fracture. However, the mechanism of hybrid fracs stimulation has still not very clear, on conditions of interbeding of sand, shale, whether is applicable or not need to be verified.Based on the hybrid fracs technology and the investigation on the stimulation mechanism at home and abroad, firstly hybrid fracs stimulation mechanism was further studied by using langmiur adsorption isotherm equation and equivalent seepage mechanism, analyzing gas percolation mechanism, stimulation mechanism, and in the case of micro fracture, the impact of sandstone, shale gas reservoir productivity by the main fracture permeability under the mode of hybrid fracs. Adopting transparent artificial fracture simulation devices and FracproPT 2007 software, they make simulation study about hybrid fracs supporting profile and fracture status. And using fracturing and acidizing conductivity test analyze the system’s ability in hybrid fracs conductivity proppant fracturing. The results showed that: ① improve fracture conductivity, fracture network complexity, control volume, can effectively reduce the pressure of shale reservoirs, gas desorption accelerate, increase productivity, thereby contributing to the rapid development of the reservoir; ② in the case of micro fracture, improve the permeability of the main fracture can accelerating the production speed of tight sandstone gas reservoirs, and improve the productivity of fractured well of shale gas reservoirs. ③ hybrid fracs can increase proppant volume to effectively support the fracture, as well as the proppant is non-uniform laid, forming a low resistance path seepage; ④ hybrid fracs can get longer supporting fracture and larger volume and the effective stimulated reservoir volume; ⑤ hybrid fracs sanding manner get higher flow conductivity than conventional fracturing sanding manner.Then, from four aspects of the reservoir rock brittle mineral content, nature fracture growing features, stress characteristics, fracability of reservoir analyze superiority of hybrid fracs in the formation. Studies have shown that: ① brittle mineral content of sandstone formation ranged from 60% to 80%, brittle shale mineral content ranged from 30% to 80%, mechanics of brittleness at around the 50%. which has the condition of forming complex fracture network, hybrid fracs has strong adaptability; ② the nature fractures in the formation sandstone is developed, shale segments natural fractures lack of development, natural fractures oriented at a low angle seam for communicating easily, has the possibility of forming complex fracture network, suitable for hybrid fracs; ③ The formation of Xu5 horizontal stresses are quite different(> 20MPa), uneasy to change by inducing stress fracture propagation direction, forming a complex fracture network, due to hybrid fracs proppant can improve the amount and the net pressure in the fracture, so hybrid fracs of the fifth member formation of Xujiahe Formation in Xinchang area has more advantages. ④ Every subsegment of Xu5 reservoir has the conditions that can be fractured by a large scale and application of high flow rate; in general, with the formation deep the crushability becoming bad, but each subsegment has its dessert distributed.Finally, according to the results of the field test, the adaptability of hybrid fracs were evaluated, smooth construction of all construction wells, XC1 well fracturing micro seismic monitored the transformation volume(8.55×107m3) and high-prodution wells XC1(7.78×104m3/d), which verified hybrid fracs in The fifth member formation of Xujiahe Formation in Xinchang area must have strong adaptability, while XC2 H haven’t have higher yield also explained. It still required to based on the mechanism of hybrid fracs increasing production and reservoir geology characteristics, make further study of hybrid fracs technology system for further optimization, such as low damage fracturing fluid systems and appropriate construction parameters.