| The proved reserves of the fractured reservoirs account for almost the half of all the proved reserves in the world, and its oil and gas production plays a critical role in the whole petroleum production. In China, the type of reservoir is also widespread in distribution, with significant quantity of OOIP. In particular, the fractured volcanic reservoirs, which have been discovered in recent years in China, proved of great potential for development.The production pattern for developing the fractured reservoirs is as follows: the large quantities of fractures found in the fractured reservoirs cut through the rocks, forming vast surface area, allowing the fluid to flow more easily from the low-permeable fundamental rocks to the high permeable channels. For the fractured volcanic reservoirs with bottom water, bottom water coning will result in significant decline in oil production and poor recovery efficiency. Thus, slowing the bottom-water coning speed in a greatest possible way is of great significance to the study of effective water control and prevention.Shixi Oilfield is located in Guertetingute Desert in the hinterland of Junggar Basin, about 140km to the east of Karamay City. Commercial oil flow was acquired in the Carboniferous volcanic reservoirs after completion of Well Shixi-1, which resulted in the discovery of this oilfield in February, 1992. In August, 1995, unitized production modes of natural recovery, inverted nine-spot well pattern(with well spacing of 565.6m), vertical wells combined with horizontal wells began in this oil field. At the early stage of production, the wells boasted high productivity with good development effect, but with the further development of this field, the wells were exposed to overall water breakthrough at present, with high water-cut rising rapidly and sharp productivity dropdown. In order to improve the development effect, we have taken such technological measures as reduction of choke size, production well shutdown and water coning control and water plugging. However, these turned out to be unsatisfactory due to various geological and technical reasons. In 1999, two infill wells was completed with the well spacing of 400m in the structural highs in the selected east district, and were put into production successively in the year 2000, but with in poor effect as well. At present, the problems existing in the reservoir development involve the high total water-cut, low ratio of total oil produced to OOIP and large amount of unproduced oil remaining in the matrix. To enhance its production effect, development countermeasures wee timely adjusted. This paper, by primarily using numerical simulation technology, focusing on the studied subject, carried out the following research work:(1) Fractured volcanic reservoir simulation geological model has been created on the basis of the research data obtained from the Cretaceous volcanic reservoir samples in Shixi Oilfield.(2) Development assumption of oil production with water drainage was proposed, by using the favorable conditions of great thickness, vertical fracture development and sufficient elasticdrive energy of the Cretaceous volcanic reservoir. Feasibility studies have been carried out on the water-drainage recovery mechanism based on the fractured volcanic reservoir simulation geological model in Shixi Oilfield, with the purpose of providing scientific theoretic basis and new method of enhancing the recovery factor in doing research in similar oil field with high water-cut(3) On the basis of the simulation geological models of fractured volcanic reservoirs, as well as reservoir fractures and interbeds distribution, water encroachment under different water invasion patterns have been studied. We made further study on the water invasion mechanism of fractured volcanic reservoirs and presented the effective water-control measures by conducting sensitivity analysis of various parameters of controlling water invasion.Overall study was conducted on the basis of the remaining oil distribution, mechanism and... |
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