| Miaogaosi Gas Field in south of Sichuan Basin which belongs to low steep fold belt in South Sichuan of sectonic province in southeast of Sichuan, is located in Hejiang County of Sichuan Province. Miaogaosi anticline is a buried anticline which is intersected by longitudinal buried fault zone and two latitudinal buried fault zones which are Naxi and Changyuanba. Gas reservoir in Maokou Formation of Miaogaosi Gas Field is fracture-cavity typed carbonate gas reservoir with water, whose reservoir is with high heterogeneity. Matrix of the reservoir is dense. Fracture-cavity system is the main reservoir and flow space. The relationship between gas and water layers is very complicated, and there is no unified gas/water contact. Currently, the development phase has proceeded to the middle-late time. Large-scale water breakthrough and deliverability declining lead to development difficulty of remaining reserves.In order to improve the level of reserves producing of Gas reservoir in Maokou Formation of Miaogaosi Gas Field, various kinds of basic data of this area were collected. On the basis of combination of reservoir geological characteristics and characteristics of development performance, a detailed analysis of what, such as characteristics of reservoir development, characteristics of reservoir fluid, model of gas and water relationship, output characteristics of gas and water and influencing factors of drainage, was conducted. And the reserves of several main fracture-cavity system was calculated. And then reasonable measures were proposed to tap the potential. The following conclusions were got through these researches:1. The pay formations of production wells of Maokou Formation in research area, which mainly growing in P1m2, are all within 200m below the exposure level of Maokou Formation, and most of them are within 120m. Those pay formations, which in 120m to 200m, are near the faults. It means that the distribution of reservoir is mainly controlled by ancient karsts and faults and fractures.2. There is always coexistence of gas and water in the fracture-cavity system. The production process is complex, and the main drive mode is gas drive. Based on detailed analysis of development performance of each fracture-cavity system, the water gas relation mold and its changes in production process were got. According to the feature of the production of water and gas, it can be divided into three types, which are water gas ratio increases, water gas ratio is stable and water gas ratio declines.3. The prime factors affecting drainage effect of single well are: reservoir conditions, separated gas reserves, water resistance, the location of the borehole reservoir and drainage method. Taking full advantage of drainage condition and choose reasonable drainage methods are important approaches of improving the gas recovery in the study area. For the multiwall fracture-cavity system, it's better for development of separated gas and development effect of hole system to choose the lower well to drainage.4. Because of the output of water was ignored in the reserve calculation of pressure drop method, the calculation accuracy was affected. Therefore, this time based on the reserve calculation of pressure drop method, the material balance method that considered the output of limited water was used for reviewing the reserve, and took it as a foundation of potential tapping.5. In view of different production specifications and different resource potentials among each fracture-cavity system, the potential tapping measures should be different too, to achieve the best tapping effects. The mainly potential tapping measures included keep Large-scale drainage of lower well, produce with low pressure difference for higher well, improve the reservoir conditions, use drainage technology such as gas lift etc., and deployment of new wells in the same well site. |
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