In the current climate, of oil price slump, native sampling and data acquisition are deemed uneconomical as oil and gas companies adopt cost rationalization to sustain business models. Exploration and development data which were previously overlooked are now being sought to gain critical. Cuttings, collected during drilling, can provide overburden and reservoir mineralogical data for better understanding of formations as well as a detailed evaluation of seal integrity for a consideration as a potential CO2 storage sites.
Through reservoir zonation and well correlation, drill cuttings were selected from respective target zones. Depending on the sample condition, necessary preparations were carried out prior to mineralogical analysis on this cutting samples. Sample age and improper preservation significantly impacted sample condition and some had to be discarded during the screening process. X-ray diffraction (XRD) analysis was carried out on selected samples which yielded semi-qualitative mineralogical data (+/- 5%). The drill cuttings mineralogy data were then cross checked with rock chips from available conventional core and well logs to observe variances and consistency.
Samples from four wells in the S field were analyzed to establish the mineralogical data. Variance of mineralogical content was observed between cuttings and rock chip samples, however mineral proportion are comparable, particularly in clay minerals, plagioclase, siderite and pyrite. Similar type of clay minerals were observed in both ditch cutting samples and core chip samples, where the total clay amount in Seal A is higher than in Seal B. Both types of samples have high contents of illite, and mixed layer (illite dominated) and minimal content of the swelling clay, smectite. Overall, results indicated similar mineralogical composition across S field cap rock in seal A and seal B intervals.
The study demonstrates the reliability of the ditch cutting samples, with proper selection and preparation, providing more extensive coverage and availability of mineralogical description over extended zones. The mineralogical information is useful for the analysts to discern the facies types and distribution, hence reducing the uncertainties.