Yanchang Zi Bei Oil Filed Long 2 Reservior Clean Fracturing Fluid Research

With the experience gained from the development of the Chang 2, Chang 6 and Chang4+5 members in the Yanchang oilfield, we found that the exploitation of ultra-low permeability reservoirs with low porosity is extremely hard and the stimulation effect is poor.The reservoir is highly heterogeneous with a low recovery rate and the individual well production is low and declines sharply. The production plateau phase is short which is uneconomical. The pressing issue facing the Yanchang researchers is how to exploit the deep-buried Yanchang formation economically and efficiently.In Yanchang oilfields, fracturing is the major stimulation to buildup the production. The performance of the fracturing fluid has direct influence on the fracturing effect and the accomplishment of the production task.To solve the problems we came across while using clean fracturing fluid in the Yanchang Zibei Chang 2 reservoir, we developed an efficient clean fracturing fluid compound. By avoiding using cationic surfactant as the base, the compound will not be absorbed to the anionic sandstone surface which may cause a rise in capillary pressure resulted in formation damage. It is a small-molecule visco-elastic surfactant compound which is convenient to blend and has no residue. The incomplete gel breaking of fracturing fluid may lower the flow back rate and cause formation damage. This compound solves this problem by using gel breaking solution which works within and without the crude oil-brine-rock(COBR) system. This new fracturing fluid can clean the residue oil adhering to the rock surface and clear out the transport path. Treated wastewater is used to make up the compound to work out the water shortage in Shanbei area. The flowing back gel breaking solution can be recycled and used as pre-flush or displacement fluid in the next fracturing operation. The recycle is of critical importance to develop the oilfield effectively and environmental-friendly.The trials involved 5 wells proved that this is a cost effective and environmental-friendly compound which provides simple operation. It has a large proppant carrying capacity, brings less formation damage and be able to break down the gel. It can be used to replace the guar gum based fracturing fluid and spread in use through the Yanchang oilfields.