深海底水气藏水侵规律与水侵风险识别方法

为了探索深海底水气藏控水开发策略，基于南海LS17-2深水气田的地质特征、水体特征及开发特征，针对水平井开展沿程产气剖面测试实验与大型3D底水气藏水侵物理模拟实验，定量分析底水脊进影响因素，在此基础上建立了适用于深海底水气藏开发的水侵风险识别方法。研究结果表明：①底水气藏开发过程中水体的脊进受到储层非均质性、生产制度、水平井筒趾跟效应的影响，并且上述3个因素对水侵的影响程度依次减小；②井区横纵比决定了气井产能是否会受到水侵风险的影响，而储层的非均质性会影响水侵风险识别界限，并且储层非均质性越强，横纵比安全界限值越小；③渗透率级差为1、10、20、30时，横纵比安全界限值依次为41.18、21.61、12.60、5.31；④基于建立的渗透率级差与井区横纵比安全界限值的关系曲线，A4H井储层平面渗透率级差为30、横纵比为77.20，远远大于横纵比安全界限值（5.31），该井受到水侵影响的风险高，必须进行控水开发。针对深海底水气藏的控水开发，提出以下策略：①通过改善水平井筒趾跟效应以及削弱储层非均质性的影响，来抑制底水的不均衡脊进，相应措施为适用于水平井的环通多级人造井底技术与变密度筛管技术；②对开采制度进行调控，以防止不均匀水侵的形成，相应措施为周期采气技术；③在井底附近建立阻水屏障，进而抑制前缘水头的脊进，相应措施为水平井充填透气阻水砾石技术；④兼容并蓄，形成各阶段相互弥补的全生命周期气藏复合控水开发技术。结论认为，该研究成果不仅可以用于储层渗透率级差介于1～30、采气速度为3%条件下的深海底水气藏水侵风险判断，而且还可以为海上、陆上底水气藏的控水开发提供借鉴。

Water invasion law in deepsea bottom-water gas reservoirs and a water invasion risk identification method

In order to explore the strategies for water control development of deepsea bottom-water gas reservoirs, this paper carried out a testing experiment of gas production profile along horizontal well and a large-scale 3D physical simulation experiment of water invasion in bottom-water gas reservoirs, based on the geological, water body and development characteristics of LS17-2 Deepwater Gas Field in the South China Sea. Then, the factors influencing bottom water coning were quantitatively analyzed. And based on this, a water invasion risk identification method suitable for the development of deepsea bottom-water gas reservoirs was developed. And the following research results were obtained. First, water coning in the development process of a bottom-water gas reservoir is influenced by reservoir heterogeneity, production system and horizontal well toe heel effect, and the influence degree of which on water invasion decreases in turn. Second, whether gas well productivity is influenced by water invasion risk is controlled by the aspect ratio (the ratio between the horizontal length of the well control area and the avoiding distance of a horizontal well) of well block. The identification limit of water invasion risk is affected by reservoir heterogeneity. And the stronger the reservoir heterogeneity is, the smaller the safety limit of aspect ratio is. Third, when the reservoir permeability difference is 1, 10, 20 and 30, the corresponding safety limit of aspect ratio is 41.18, 21.61, 12.60 and 5.31, respectively. Fourth, based on the relation curve between permeability difference and safety limit of the aspect ratio, the areal reservoir permeability difference of Well A4H is 30 and its corresponding aspect ratio is 77.20, which is much higher than the safety limit (5.31) of the aspect ratio. It is indicated that the well has high water invasion risk, so water control development is inevitable. Finally, the following strategies were proposed for the water control development of deepsea bottom-water gas reservoirs. First, improve the toe horizontal well heel effect and weaken the influence of reservoir heterogeneity so as to restrain the unbalanced coning of bottom water. And the corresponding water control measures include connected multi-stage artificial bottom hole technology and variable-density screen technology suitable for horizontal wells. Second, adjust the production system to prevent the formation of nonuniform water invasion. And the corresponding water control measure is the periodic gas production technology. Third, build up a water blocking barrier near the bottom hole to inhibit the coning of frontal water head. And the corresponding measure is the water permeable and water blocking gravel packing technology of horizontal well. Fourth, combine these measures comprehensively to form a complementary composite water control development technology for the whole life cycle of a gas reservoir. In conclusion, the research results not only can be used to judge the water invasion risk of deepsea bottom-water gas reservoirs with the reservoir permeability difference of 1–30 and the gas recovery rate of 3%, but also can provide reference for the water control development of offshore and onshore bottom-water gas reservoirs.