P₁S₂ Reservior Heterogeneity Evaluation Of Yu Lin Gas Field In Ordos Basin

Whether the reservoir is good or not has an important effect on gas well deliveriblity and gas field development policy determination and its final recovery ratio.The Yulin Gas field is one of the largest gas field in Ordos basin with a big gas-bearing area and low richness of OGIP and low permeability. The Permian Shanxi Formation (P1s) is typically 90-120m thick and divided into two parts (P1s1 and P1S2). The sedimentary facies of the main Reservoir(P1S2 in Shanxi Fm) generally is braided distributary channel sediment. The river change its flow direction frequently, So this kind of sediment facies leads to complicted sand body, the reservoir properties shows high heterogeneous.On the basis of the existed research result, through the use of the seismic, logging, drilling, geology and production test data, this paper mainly focus on the distribution of P1s2 sand body, the analysis of how the sedimentary facies controlled the sand body, the eservoir heterogeneity appraisal that was controlled by sedimentary facies and sand body, the heterogeneity appraisl includes micro heterogeneity(pore throat heterogeneity and grain heterogeneity)analysis, interlaminar heterogeneity analysis. According to this, the paper applied one of the geostatistical analysis methods—Variogram function, to forecast the single sandscale and describe the distribution of the P1s2 sandbody. On the basis of the analysis of the permeability tensor with Darcy's law, evaluated the peimealibity anisotropy, Finally builded the P1s2 reservior model.The studies shows: First, The Quartz Arenite sand reservoir was deposited in a high energy braided river system, giving a high level of lateral continuity. This is demonstrated by the consistent presence of P1s2 Quartz Arenite sand in all wells drilled within the Yulin gas field, together with observations from outcrop studies. The gross sandstone unit comprises amalgamations of sand channels. Shale breaks mayseparate individual sand channels vertically, P1s23 sandstone is fine and distribute steadily with good connectivity and large thickness, The lateral distribution of P1S2 sandbody like a belt extend from North to South with the channel control, and The reservoir quality of P1S23 formation depends on the steady distribution of the P1S23 sandsone. Second, The micro heterogeneity, interiorlayer heterogeneity and interlaminar heterogeneity analysis shows that the Clean, coarse grain sandstones which show a favourable effect on reservoir quality in the Quartz Arenites , so the coarse grain sandstones and the pure lithology are the basis and the good pore combination is the key factor of the effective reservoir. Third, applied the variational function to the analysis of the reservoir property variety predication in three dimension, and the last, It is valuable and useful for low permeability gas field development to use the Darcy law and the permeability tensor analysis to describe the Permeability anisotropy.