Impact of Oil Based Mud on Chemo-Mechanical Properties of Cuttings and its Treatment

Abstract

ABSTRACT: In this study, we investigated the chemo-mechanical properties of cuttings contaminated with oil-based mud (OBM) and its various treatments. Rock fragments are obtained from Eagle Ford and Marcellus formations, which are then cut into cuttings with sizes ranging from 4 mm to 8 mm. The Eagle Ford sample is a carbonate-rich organic free sample, while the Marcellus sample contains a mixture of Calcite, quartz, and clay. We contaminated each sample with OBM under controlled pressure and temperature conditions. We then cleaned the samples using several treatment methods: wiped with cotton buds, soaking in a solvent, and soaking in diesel. Chemo-mechanical properties before and after contamination of each sample were then studied using micro-indentation technique and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). In doing so, the analysis was performed on samples’ cross-sections to study properties changes across the depth of contamination. A discussion on mechanical and chemical evolution across the sample depth will be presented. Degradation in mechanical and compositional properties are observed most severely on samples treated by solvent soaking. Wiping off OBM from the samples surface was found to preserve samples’ chemo-mechanical properties the most. Higher cuttings to OBM contamination ratio and higher cuttings to solvent ratio were observed to have more adverse effects on cuttings integrity. 1. INTRODUCTION Completions quality is an essential factor in evaluating the economic viability of a reservoir. Completions quality relies on a good understanding of rock mechanical properties (i.e., elastic, strength, and fracture properties), the in-situ stress magnitudes, orientations, anisotropy, and rock mineralogy to determine the most effective completions design and treatment (Prioul et al. 2016, 2018). Typically, these properties are measured through laboratory testing on cores, outcrops, and well logging. Though cores are preferred, they are only acquired on a select number of wells due to cost and are typically taken on the vertical section of the wells. Well loggings are usually performed on select wells during the exploration phase and are limited to acquisition resolution. Drill cuttings, however, are continuously collected and transported to the surface throughout drilling and are available throughout the vertical and lateral sections of the well at no additional cost. Cuttings have been shown to be a valuable resource for determining petrophysical properties (i.e., permeability, organic content, porosity, density, mechanical properties) in cases where cores collection and logging are not economically viable and technically challenging (Ortega et al., 2012; Olusola et al., 2014; Prioul et al., 2016; Althaus et al., 2020; Sanei et al., 2020).