Study On Reservoir Fracture Closure In Yijianfang Formation, Ordovician In Tahe Oilfield

Tahe Oilfield Tuofutai Ordovician reservoir is typically fracture-cavity carbonatereservoir，cracks，caves are very developed，almost no reservoir matrix infiltrationcapacity. This year ’s study shows that this reservoir has a strong heterogeneity，production decline curves are unstable，geological understanding has a low level. Tothe end of December2011，Production Plant3had101wells stopped，47of them usedto be production wells，the rest54wells has never been a production well; in these47production wells，26of them have been high-yield wells at the beginning，21of themhave been stripper wells since early completion. These101wells accounted for28.1%of the total360wells of the production plant3，how to tap the potential of these wellsis a key issue to achieve efficient development of oil fields. In the early exploration anddevelopment process，people believed that the main fracture types are horizontalfractures and low-angle fractures in this area，and because the reservoir was burieddeep，mining fast，these fractures are easy to close. This article is to test the idea，and evaluate the influence of fracture closure during the production of the oilfield.Through the detailed research on the geological feature and exploration anddevelopment process of Ordovician oil in Tuofutai of Tahe Oil Filed. In addition，bymeans of sufficient survey and systematic processing of theories，experiments，andon-site examples related to crack closure，the research achievement is made on thebasic feature of the crack closure and the key factor influencing the crack closure isfound. Then，according to the geological situation and development situation of Tufutaiof Tahe Oil Field，combing with the influencing factors of crack closure，a targetunderstanding of the reservoir feature of Tuofutai is obtained. In the end，based on thenew understanding， the development feature of developed oil well is analyzedcomprehensively. Besides，the influence of crack closure on development features ofvarious oil fields is evaluated for the following conclusions.(1) During the reservoir development process，the fracture closure is an objectivephenomenon. A large number of indoor experiments of fracture closure of carbonaterocks show that when the pressure is increased to cover several MPa cracks hadchanged greatly，in the development process of Tahe Oilfield，many wells that drilled smaller or less energy reservoir have reached10MPa or more，and even declined insome wells20MPa or more.(2) In this area，cave、fracture-cave reservoirs is developed，in these two typeof reservoirs，capacity and permeability，the role played by the crack can not beaccounted for dominance. Most of the fracture reservoirs has a low deliverability anddid not turn to a production well. This phenomenon is caused by human factors，in thecourse of locating wells，people generally choose more developed reservoirs aroundthe big break or predictable intervals caves are developed，this process objective avoidthe reservoirs that cracks are in the dominant. As the carbonate fracture-cave reservoirtake fracture-cave units that is surrounded mostly by matrix as mining unit，so thedevelopment performance has a strong independence，the unit is dominated by whatreservoir the unit was dominated，it showed what kind of development feature，whichis different from other fractured reservoirs.(3) Development of the low angle fracture of this reservoir is far less rich thanimagination. We observed that in most of the hole sections segment observed thatmulti-angle fractures cross combined to form a mesh system，the extent of fractureclosure should be low in these interval，which in some extent，reduce the effects of lowangle fracture closure.(4) Production performance of Tuofutai Ordovician reservoir of Yijianfangformation was mainly controlled by the volume of the cave，as well as the energy levelof the reservoir，the influence factor，fracture closure plays a unimportant role in thisphenomenon; production performance of fracture-cave reservoir is mainly controlledby the reservoir size and the level of the reservoir energy.(5) Fracture closure of the entire field have little effect on energy produced.Similar vuggy carbonate reservoirs like Tuofutai area，its main production wascontributed by cave reservoir and fracture-cave reservoir，these reservoirs have a lowsensitivity of stress; and most wells of Tuofutai area are acid fracturing completion，which to some extent also reduced the impact of fracture closure.