Successful Applications of SEM-Based Formation Evaluations While Drilling

Abstract

Abstract

LWD Gamma Ray is commonly used for Geosteering in a tight shale reservoir; however, the measurement has anisotropic interpretation for the formations. It is because Gamma tool measures three radioactive elements in formations: potassium, uranium, and Thorium. The anisotropy can make people misled. For example, when LWD detects high Gamma, it may mislead the LWD engineers to deem they drill in“good” shale, which actually they may drill in the high potassium, not high uranium shale (high organic content). This results in a problematic fracturing, and missing the fracable sweetspots. In the Sichuan Shale China, the authors witnessed such “misleading”, and will present several cases in the paper to address the problem. With LWD Gamma data, the people is hard to extract the information in regarding with rock fracability whilst drilling, and thence be less benefit for fracture optimization. In addition, Wireline has high risk and operational cost to acquire the data in long lateral horizontal wells.

Hence, the SEM-based cutting analysis shows its power to solve the problems. The case study shows that, compared with conventional LWD and wireline measurements, the wellsite cutting-based fast analysis has low risk for enhanced reservoir navigation, and a better definition of mineralogical, elemental and textural heterogeneities throughout vertical and lateral wells. It will allow a more cost-effective completion optimization (stage placement, perforation, and clusters).

This paper introduces minerals and elemental analysis approach in Geosteering. It is reactive approach to evaluate the shale fracability using wellsite-based SEM technology. The cuttings are scanned at the wellsite to get various elements and minerals, such as quartz, clay minerals, carbonates, as well as rock texture data. By comparing LWD Gamma and Elemental Gamma, the geologist is able to consist the samples depth to control the data quality, meanwhile, extract abundant formation information to navigate in drilling.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016