Study Of Low Damage And High Efficiency Hydraulic Fracturing In Low Permeability Unconventional Tight Reservoirs

The development of unconventional resources have achieved revolution from"unconventional resources"to"conventional resources" in North America. In contrast, China’s unconventional tight gas reservoirs are widely distributed. The exploration potential is tremendous. By the end of 2011, unconventional tight gas resources 1/5 accounts for the national total gas resources. Reservoir stimulation technology is"killer mace" for the development of unconventional industrialization. Due to the special features in pore, rock characteristics and development model, studying of low cost, efficient unconventional tight reservoir simulation technology has important academic value and commercial value.Based on the point of "dynamic and static"and "macro and micro" ideas, using such as rock mechanics, fracture mechanics and fluid mechanics, this dissertation focuses on the study of fine reservoir evaluation, damage mechanism and optimization design of stimulated reservoir volume(SRV), combination with core experiment, mechanism research and field application. The highlights of the research works including:l.In unconventional tight gas reservoir evaluation, in addition to drilling, logging, X-ray analysis, environmental scanning and rock dynamics, new methods including CT magnetic scanning, constant mercury pressure and brittleness index were put forward.2.Considering non-Darcy effect of fracture simulation method, gas conductivity evaluation method was put forward in unconventional tight gas reservoir. Using fracture mechanics and fluid coupling method, a new mathematical model of fracture face skin with segmentation characteristic was built conforming to classical theoretic model of PKN and KGD. It has an important theoretical guidance for the improvement of post-fracture production which has higher innovation.3.On the study of optimization SRV treatment design, based on"divert hydraulic fracturing"and"network fracturing", through mechanics and fluid and solid coupling analysis, the two horizontal stress was analyzed. The horizontal stress difference was decreased using force close, quickly flow-back and multiple treatment, so the fracture can be diverted. In case of Sulige, selection chart was built according to stress shielding performance, meanwhile, ball blocking density difference and ball blocking efficiency relation chart and displacement and seat sealing relationship chart were built. A new principle considering SRV in horizontal well was proposed in order to maximize oil drainage volume as objective function. The design of horizontal well length, number of segments, parameter optimization were analyzed on the basis of vertical wells design, The main fractures and branch fractures matching relation in volume fracturing has also been studied. This study has certain forward-looking and field operation.Overall, a preliminary systematic fracture technology of unconventional tight gas reservoirs was studied and put forward in the paper, which has a great significance in improving fracturing technique level and development level of other unconventional resources as well.