鄂尔多斯盆地低渗透—致密气藏储量分类及开发对策

鄂尔多斯盆地低渗透—致密气藏储量规模虽大,但储层物性差、非均质性强、储量动用程度低且差异大,要实现气藏的长期稳产及效益开发难度大。为此,以该盆地5个主力气田为研究对象,以效益开发为导向,以内部收益率为核心评价指标,结合动、静态特征对低渗透—致密气藏进行储量评价单元划分、储量分类评价和储量接替序列的建立,并针对不同类型的储量提出相适应的开发技术对策。研究结果表明:①该盆地单井动态储量小、产气量低,产气类型可以划分为多层协同供气和单层主力供气两种;②基于地质条件和单井动态特征相近的原则,结合开发管理区块分布情况,将该盆地内5个主力气田划分为11个储量评价单元,以内部收益率30%、8%和5%作为界限,把储量评价单元划分为高效、效益、低效和难动用4种储量类型;③以内部收益率8%为有效开发的基准,将其对应的井均估算最终开采量(EUR)与各个储量评价单元实际的井均EUR对比,按照效益由高到底的顺序,建立了储量评价单元经济有效动用序列;④高效储量适宜采取增压开采和局部井网调整对策,效益储量需通过井网加密提高储量动用程度,低效储量应采取富集区优选、滚动开发对策,难动用储量需加大技术攻关以实现效益开发。结论认为,该研究成果有助于提高鄂尔多斯盆地天然气储量的动用程度,可以为该盆地天然气长远开发战略的制订提供技术支撑。

Reserves grading classification and development countermeasures for low-permeability tight gas reservoirs in the Ordos Basin

Low-permeability tight gas reservoirs in the Ordos Basin are characterized by poor reservoir physical properties, strong heterogeneity, low reserves producing degree and large difference in reserves producing degree, so even though their reserves scale is large, it is still a big challenge to keep long-term stable production and efficient development. To this end, this paper took five main gas fields in the Ordos Basin as the research objects to carry out reserves evaluation unit classification, reserves grading classification and evaluation and reserves developmental sequence establishment on low-permeability tight gas reservoirs by taking the benefit development as the orientation and the internal rate of return (IRR) as the key evaluation index, combined with dynamic and static characteristics. Furthermore, development technical countermeasures were put forward correspondingly for each type of reserves. And the following research results were obtained. First, the Ordos Basin is low in single-well dynamic reserves and gas production rate, and its gas producing patterns can be classified into two types, i.e., multiple-layer cooperative gas supply and single-layer main gas supply. Second, the five main gas fields in the Ordos Basin are divided into 11 reserves evaluation units, based on the similarity principle of geological conditions and single-well dynamic characteristics, combined with the distribution situations of development management blocks. And then by taking IRR of 30%, 8% and 5% as the boundaries, the 11 reserves evaluation units are classified into four reserves types, including high-efficiency, efficiency, low-efficiency and difficult-to-produce. Third, with IRR 8% as the threshold of effective development, the corresponding estimated ultimate reserve (EUR) per well is compared with the actual EUR per well of each reserves evaluation unit. And according to the benefit order from the top to the bottom, the cost-effective developmental sequence of the reserves evaluation units is built up. Fourth, it is suitable to apply pressurized exploitation and local well pattern adjustment to high-efficiency reserves, well pattern infilling to middle-efficiency reserves to increase the reserve producing degree, enrichment region selection and progressive development to low-efficiency reserves, and intensive technological research to difficult-to-produce reserves to realize benefit development. In conclusion, the research results are conducive to improving the producing degree of natural gas reserves in the Ordos Basin and provide technical support for the preparation of the Ordos Basin's long-term natural gas development strategy.