The Analysis and Assessment of Two-Dimensional NMR Technology in Shale

Abstract

The gas shale reservoir has many characteristics unlike other conventional resources, generally including Nano pores, super low permeability, non-Darcy flow, self-source-reservoir and successive accumulation. in this paper, the NMR instrument has been improved, (1) increasing the magnetic intensity, (2) shortening the echo interval, (3) optimizing the pulse sequence and acquisition parameters. Through the improvements, the pore structure resolution has been increased by ten times. In one-dimensional spectrum, the pore fluid signal can be detected beyond 1.5nm diameter and in two-dimensional spectrum. The pore fluid signal can be detected beyond 300nm diameter. The shale pores can be divided into three types including organic pores, mineral matrix pores and micro fractures. The diameter distribution of these pores can overlap and extend widely. The results show that the short relaxation peak show the organic pore generated by the kerogen before the 10ms of T2. But the relaxation peak between 10 and 100ms represent the micro fractures. Combined with the former studies, the pore structure model has been built to identify the organic pore; mineral matrix pore and micro fracture and evaluate the pore structure, total porosity and effective porosity. Affected by the internal gradient, diffusion and wettability, the two-dimensional spectrum model is not similar with that of conventional reservoir. The correlation between the diffusion and T2 values of the oil, gas and water show non-linear. Integrated with the pore types and scale, the interpretation model have been used to distinct the bound fluid, free fluid and identify the oil, gas and water. Organic pores is directly correlated with the organic carbon content, kerogen type, maturity, generation hydrocarbon intensity, generated pressure and absorbed gas content. The mineral matrix pores reflect the compaction and the free gas content. The micro-fracture show the pressure intensity of structural compression and generation hydrocarbon, the free gas and oil content, and the natural fracture network of volume fracture. So these can evaluate the reservoir quality. Above mentioned results have been applied in Bonan sag and western Sichuan basin successfully.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015