ABSTRACT:

Carbonate reservoirs have a significant proportion of the known petroleum reserves, with its characteristics of pores and fractures development. A series of laboratory testing have been performed. Using high pressure water jet cutting the artificial crack (different angles and different lengths for dolostone & limestone), in order to simulate the natural fractures. We have measured P-wave velocity and S-wave velocity on carbonate rock for original specimens and artificial crack specimens. Results from laboratory research are as follows: 1) as the fractures exist, P-wave velocity and S-wave velocity decreased, the fracture has more influence on S-wave velocity than P-wave velocity; 2) under uniaxial compression, the curves of axial strain and the compression velocity can be divided into three stages: 3) the fracture has an important influence on mechanical parameters of carbonate rock. Increasing fracture angle and length will result in decreasing the strength parameters under uniaxial compression; 4) under condition of confining pressure, P-wave velocity increases with the increasing of confining pressure. The growth rate of dolostone’s P-wave velocity is larger than limestone. The research results can be used for better analysis the mechanical and acoustic wave characteristics of carbonate rock in deep drilling engineering and provide technology parameters for exploration in carbonate reservoirs.

1. INTRODUCTION

With further exploration and development of oil and gas, the strategic of oil and gas resources has changed direction to deep formation field. Therefore, the rock mechanics problem of carbonate sediments has become a hot topic studied. There are almost 300×104km2 carbonate formation distribution in China, most of the them have complexity characteristic, such as extended span of time, extended span of deep-buried, strong heterogeneity, fracture-pore development and other factors. The variations of rock mechanics parameters of carbonate formation are not easy to master.

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