莺歌海盆地中深层天然气勘探的关键问题及对策

Key challenges and strategies for the success of natural gas exploration in mid-deep strata of the Yinggehai Basin

现阶段莺歌海盆地中深层天然气勘探面临3个关键问题:①强超压层系内天然气是否可以成藏;②中深层沉积体系复杂,优质储层分布规律不清;③储层评价和烃类检测技术遇到瓶颈,储层含气性不易识别。经深入分析近年中深层高温高压钻井和勘探实践,认为烃类气已在中深层聚集成藏,但储层物性较差,因此,寻找优质储层是当前天然气勘探取得突破的关键。策略上,一是要利用地震沉积学的方法和思路寻找有利相带,预测优质储层;二是要进行储层类比研究,充分认识储层内非均质性引起的物性变化,探索优质储层的分布规律;三是要以岩石物理研究为基础和桥梁,利用高精度三维地震资料尝试叠前地球物理反演研究,增强烃类检测的可靠性,提高气层预测的精度。

Three key problems confronted with the natural gas exploration of mid-deep strata in the Yinggehai Basin were discussed here： ①whether natural gas can accumulate in super-overpressure strata;②within a complicated sedimentary system of mid-deep strata,distributional disciplines for high-quality reservoirs are hard to be mastered;③reservoir evaluation and hydrocarbon detection techniques encounter a choke point to be improved,which in turn leads to difficulties of gas identification in reservoirs.Drilling and prospecting practice in high-temperature and high-pressure mid-deep strata in recent years demonstrated that gaseous hydrocarbons could have accumulated in mid-deep strata,where,however,reservoirs developed with poor porosity and permeability.Therefore,the key to the success of natural gas exploration in these strata is to find high-quality reservoirs.Strategically,a couple of policies gaining access to the success of natural gas exploration were proposed as follows： firstly,to look for payable facies belts and predict good reservoirs by using approaches of seismic sedimentology;secondly,to fully understand variations in physical properties caused by heterogeneity in reservoirs and search for distributional disciplines of good reservoirs by analogy with various reservoirs;and thirdly,to use high-precision 3D seismic data to try prestack inversion on the basis of petrophysical studies so as to improve the reliability of hydrocarbon detection and the precision of gas reservoir prediction.