The Study On The Fracture Potential Of Yushulin Oil Field

Yushulin Oil Field is located at the eastern slope of Sanzhao depression in the northerncentral depression of Songliao Basin, which has millions of tons reserves around Daqing. Itsoil-bearing area is314.1km~2and original oil in place is18748×104t.As a peripheral ultra-low permeability oilfield, after years of waterflooding development,Yushulin Oil Field has already went into middle stages of oil-field development. Since1999,with the remaining reserves in undeveloped areas has low abundance, poor physical property,geological conditions and development technology are restrained, various contradictionsbecome more prominent, such as the development of remaining reserves is difficult to use, therising velocity of water in the development areas has been speeded up and declining rate ofproduction of old wells has been increased, all these show that there are several difficulttechnical problems crying out for solutions. As an important technology to increaseproduction of single well, fracturing technology has played an important role in thedevelopment of Yushulin Oil Field. However, like other similar oilfields, there are manyissues related to fracturing technology need to be answered, such as the potential ofreconstructing of reserves, the factors affecting the effect of fracturing on oil wells, andwhich of these are more sensitive to the development of the field under the presentdevelopment conditions. To scientifically, timely and correctly answer these questions, basedon the development of current fracturing technology, it’s necessary to carry outcomprehensive research on the present exploitation situation of oilfield and the potential ofreservoir fracturing, and analyse the facilitation and adaptability of existing advancedtechnology for oil-field development, which will provide technical support for scientificdecision making and ultimately enhance the production level and economic benefit.Through studying on the regional stratigraphic structure and geologic characteristic ofthe reservoir, Yushulin Oil Field is fault-lithology composite reservoir, which is affected bylithology and fault. Because of sedimentation, main sandstone-developed zone existssandstone-undeveloped area or physical properties changing area, the connectivity betweensandstones is poor, there always appears oil-free sandstones or sandstones with lowoil-bearing levels. This area mainly develops Fuyu and Yangdachengzi oil layer of LowerCretaceous sedimentary reservoir. Fuyu oil layer is of lithic arkose and feldspathic lithicgreywacke, and Yangdachengzi oil layer is of lithic arkose. According to the reservoir properties, development of fracture, effective thickness and oil-field development situation,the Fuyang layer is divided into ClassⅡ and Class Ⅲ blocks. Because fracture is developed,average permeability and effective thickness is relatively higher, Class Ⅱ blocks can forman effective water drive pressure system during water-injection development. Most of classⅢ blocks are difficult to form an effective displacement system during water-injectiondevelopment, because of the poor physical property, intensive heterogeneity and pooradaptability of well networks. Relative permeability characteristics indicate that theirreducible water saturation and the residual oil saturation after water flooding are high, therange of oil-water permeation is narrow, and the oil displacement efficiency is low.Through assessment and analysis to the wells fractured in Sheng382block and Shu322block of Yushulin Oil Field, we find out the rupture characteristic of rock, filtration propertyof reservoir, difficulty level of sand fracturing, and effect of fracturing, which is attribute tocognition the feasibility and potential analysis of fracturing in the field. The effectivepermeability of the oilfield is determined after studying on production dynamic historymatching on the four wells of Sheng382and three wells of Shu322. Combining with invertednine-spot pattern, the effects of different fracture lengths to production at differentpermeability was studied, which can be help to parameters design of fracturing jobs. At thesame time, based on the optimized fracture length, the effects of formation pressure, effectivepermeability, effective thickness, reservoir pressure, and oil viscosity to fracturing wasstudied, which can provide a reference to select wells to be fractured.Through the evaluation of geological characteristics of reservoir fracturing, research onprevious fracturing material and characteristics, fitting on production dynamic history, andanalysis on effect factors of fracturing in oil wells shows that it’s necessary and feasible tocarry out fracturing reconstruction for Yushulin Oil Field, associating with present materialbase of the field and advances in technology, as well as a large number of simulationresearches, relevant circumstance of increasing production and efficiency in this thesis alsosupport the view before. Hydraulic fracturing technology has an extremely important strategicsignificance in the development of the field.