Multifractal Characteristics and Classification of Tight Sandstone Reservoirs: A Case Study from the Triassic Yanchang Formation, Ordos Basin, China

Zhihao Jiang,Yujiang Shi,Daxing Wang,Zhiqiang Mao

doi:10.3390/en11092242

Abstract

Pore structure determines the ability of fluid storage and migration in rocks, expressed as porosity and permeability in the macroscopic aspects, and the pore throat radius in the microcosmic aspects. However, complex pore structure and strong heterogeneity make the accurate description of the tight sandstone reservoir of the Triassic Yanchang Formation, Ordos Basin, China still a problem. In this paper, mercury injection capillary pressure (MICP) parameters were applied to characterize the heterogeneity of pore structure, and three types of pore structure were divided, from high to low quality and defined as Type I, Type II and Type III, separately. Then, the multifractal analysis based on the MICP data was conducted to investigate the heterogeneity of the tight sandstone reservoir. The relationships among physical properties, MICP parameters and a series of multifractal parameters have been detailed analyzed. The results showed that four multifractal parameters, singularity exponent parameter (αmin), generalized dimension parameter (Dmax), information dimension (D1), and correlation dimension (D2) were in good correlations with the porosity and permeability, which can well characterize the pore structure and reservoir heterogeneity of the study area, while the others didn’t respond well. Meanwhile, there also were good relationships between these multifractal and MICP parameters.

Highlights

Since advanced technologies of hydraulic fracture and horizontal wells were developed, tight sandstones have drawn much attention due to their considerable hydrocarbon productivity [1,2].Different from conventional reservoirs, it is the pore structure that controls flow capacity, producible pore volumes and production capability of tight sandstone reservoirs, rather than total porosity [3,4].Tight sandstone reservoirs often have strongly laterally and vertically heterogeneous pore structures, expressed as a big and fast change in porosity and permeability
The porosity and permeability (K) values of the samples are listed in Table 1, together with a series of mercury injection capillary pressure (MICP) parameters
The permeability ranges from 0.108 mD to 9.987 mD with most of them less than 1 mD, and tight sandstone

Summary

Introduction

Different from conventional reservoirs, it is the pore structure that controls flow capacity, producible pore volumes and production capability of tight sandstone reservoirs, rather than total porosity [3,4]. Tight sandstone reservoirs often have strongly laterally and vertically heterogeneous pore structures, expressed as a big and fast change in porosity and permeability. Accurate description of the pore structure of tight sandstone is conducive to evaluating the productivity of reservoirs and searching for remaining oil [5,6,7,8,9]. The diagenetic transformation of tight sandstone reservoir is strong, and the types of diagenesis are complex and varied, mainly including mechanical compaction, cementation and dissolution. Varied sedimentation [7], diagenesis [8,9] and tectonism [10] will lead to Energies 2018, 11, 2242; doi:10.3390/en11092242 www.mdpi.com/journal/energies

Methods

Results

Conclusion