| With the increasing development of global economy,the demand of crude oil in the world has dramatically risen.Following the extensive development of conventional oil in the last century,people have paid more attention on the abundant heavy oil and extra heavy oil resources,and as well the heavy oil production technology.Canada contains the largest heavy oil and extra heavy oil resources in the world,and then Venezuela,Former Soviet Union,Middle East, United States,and China. At present, China has been found more than70heavy oil fields in12basins. The largest heavy oil reservior is Liaohe oil region in the northeast, and then Karamay oil region in the northwest, Shengli Oilfield in the eastern.Heavy oil is very difficult to be produced by conventional technology because of its high viscosity and poor flow ability. From the beginning of viscous crude development in1950’s, many forms of development means mainly based on thermal dynamics have been set up. And the cyclic steam stimulation covers most developing conditions. The cyclic steam stimulation in heavy oil production is an effective way. A few years ago, the world began to use cyclic steam stimulation method for recovering heavy oil reservoirs, and achieved very good results. Since the1980s, China has had the promotion and application of cyclic steam stimulation technology in Liaohe, Xinjiang, and Henan heavy oil reservoirs, and has made remarkable economic and social benefits. However, after a long time of development, the yield in the block declines rapidly and economic efficiency obviously becomes poor, so it is necessary to work on improving exploitation effects of heavy oil reservoir.Extra-heavy oil is art important part pf the heavy oil resources, which is estimated to be in amount of500million tones as proven reserves in China. With comparison to the similar types of reservoirs abroad (average burial depth of200m), the depth of reservoirs in China is relatively deep (average700m). This increases difficulties in development. The cyclic steam stimulation process is commonly applied as the initial recovery technology.With the development of drilling technology, the technology of thermal recovery for horizontal well in extra heavy oil reservoir is more widely used in exploitation. In contrast to vertical well, the horizontal well has more advantage in exploitation because it increases the contact area with reservoirs and improves the capacity of injection and production of reservoir. At the same time, period production output and period OSR are increased. So the application of horizontal well can earn more economic benefit.Fengcheng oilfields of the Junggar Basin possesses a very rich shallow layer extra-heavy oil resources.The reservoir has high reserve abundance (519.6×104t/km2), shallow buried depth, low formation temperature, low formation energy, short cycle production time, low gas/oil ratio and poor economic results.In the early stage of cyclic steam stimulation, the production is high but decrease progressively is rapid. The crude oil has high viscosity (50℃-13768mPa. S), solidification point features.Extra-heavy oil reservoir of Fengcheng oilfield Zhong32well field Jurassic system Qigu group is located in the west of Fengcheng oilfield in the western part of the Junggar Basin. Scale implementation of the horizontal well make a contribution to the heavy oil stimulation in Fengcheng oilfield operational zone.But it also exposed some problems: oil viscosity is high, the horizontal well production cycle is short; injection and production parameters are not reasonable, economic indicators is low; the horizontal segment absorption of vapor is uneven and the producing degree difference is large; stimulation step is not clear.In order to improve the extra-heavy oil development effect of the horizontal wells, and to provide the basis for optimal deployment and injection/production method of follow-up of horizontal wells. In this paper, based on the research of cyclic steam stimulation recovery mechanism, the development status, characteristics and regular patterns of Fengcheng oilfield Zhong32well field Jurassic system Qigu group have been re-recognized, the main contradiction in the production of horizontal wells has been identified and the influencing factors of the effects of horizontal wells have been analysed:Including the geological condition, design parameters, injection-production parameters; The injection/production parameters have been Optimal Designed used the production dynamic analysis and numerical reservoir simulation theory:Sensitivity analysis of the following parameters including bottom dryness fraction, steam injection velocity, steam injection intensity, soaking time, fluid production velocity, production factor and cycle of conversion of steam huff-puff to steam drive are made and optimization of steam injection parameters is carried using multi-index optimization method:Steam injection intensity is the most sensitive parameter which affect the production effect in the horizontal well injection/production parameters. Steam injection intensity is directly related to the cycle steam injection amount and economic efficiency. In the same injection amount, the bottom dryness fraction greater, the greater the value of the enthalpy, the greater heating radius, the more oil production, the higher oil/gas ratio. The steam injection rate is the key parameters affecting the heat loss. Using a combination of vertical wells and horizontal wells at the right time to turn the steam stimulation to drive can gain a good development effect, but the horizontal wells network directly turn to steam drive gain a bad consequence; Profile utilization degree has been evaluated used Outcome of reservior model building and temperature profile test data of the horizontal wells, reservoir heterogeneity (permeability variation coefficient、advance coefficient、permeability differential) and profile utilization degree have been researched and the feasible measures of profile utilization degree improvement have been propsed: the horizontal well multipoint steam injection technology、the ternary combination huff-puff technology, the ternary combination huff-puff combined with double-tube steam injection technology、vertical wells and horizontal well cyclic steam stimulation technology、HDCS high efficiency exploitation technology; On this basis, the extra-heavy oil horizontal well stimulation methods have been fully invested and Suggestions of adjustment scheme have been propsed.The technology studies provide technical support for the various types of cyclic steam stimulation of heavy oil reservoirs, and can guide the actual development of the cyclic steam stimulation reservoirs. |
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