Hydraulic Fracturing Technology Study For Thin And Lower Penetrability Zones Of Daqing Oil Field

Daqing Oilfield is the biggest offshore oilfield, which plays an important role in China economics. Along with the continuous water-flooding development, the water ratio of high permeable zones rises continuously. In some blocks the water ratio is over 90%, which directly affects the oilfield development efficiency and oil production from the old blocks. To keep the high and stable production, we enhance the development of poor and thin pay zones and explore of marginal oilfield.The pay zones in second & third infill wells are thin and poor pay zones, which acted as barriers during the past development. With the development of fracturing technology for thin and poor quality zones, these zones can be further developed and add to oil the production.The success of fracturing technology for thin and poor quality zone not only raises the level of fracturing technology in theory but also improves the oilfield development in practice as well as increases the recovery ratio. It solved the problems of fracturing efficiency and barrier-protection. The production is improved and the water cut in some wells is decreased. This technology resolves the following difficult problems:1. The problem of thin barrier protection with pressure balance is resolved. With practical study, the distribution of pay zones and barriers is fully recognized and analyzed and the theory of thin barrier protection with pressure balance forms. Simulative analysis is carried out to study the stress condition of barriers which builds the theoretical base of protection with pressure balance.2. Through the stress analysis of barriers and fracturing practice, the necessary thickness for fracturing is decreased. The pay zones in the infill wells are mainly thin and poor quality zones and interlaces with the thick zones. They have lower permeability and smaller thickness. The designed barrier thickness directly affects the development thickness and productivity. So the decreased thickness of necessary for fracturing increases the thickness of production zones and oil production.3. The problems of multi-zone, large space between target zones, and difficult isolation between zones are resolved. Aiming at the features of the new drilled infill wells which have thin pay zone thickness, low permeability and many pay zones, the limited-entry fracturing method is designed, which achieves over 10 tons productivity in general wells and 20 tons at early stage in some wells. At the same time the problem of generally rising water ratio is restrained.4. The problem of fracturing thin zones in old wells is resolved. With the specially designed positioning fracturing tools and the combination of packers and sand-blasters, the number of thin pay zones needed to fracture is controlled and the barrier protection with pressure balance is achieved so as to stimulate the reservoirs.