Coring not Boring

Abstract

Coring and core analysis are considered the only direct and physical data to provide a true reflect to the reservoir properties. The measured properties are used to calibrate subsurface models and ensures close to reality properties. Representative data is critical to allow achieving such target. Coring planning and close follow up from the day decision is taken to core is important to achieve representative data. The approach followed in this manuscript allowed a high probability of successful core cutting, and representative core analysis. Field A is planned for appraisal phase and reservoir is expected to be of low permeability with sequence of shaly sands which adds complications to achieve the objective in cutting and analyzing the core. Different coring technologies were evaluated against the main coring objective of potential hydraulic fracturing field development. Conventional core is selected to offer the best value in both cost, and data coverage in compare to sidewall core. However, due to financial impact only one run was allowed, consequently it was critical to get the highest possible recovery and highest quality in one shot. An extensive planning phase investigated all variables to ensure high recovery. Rock strength and its mechanical properties allowed the selection of optimum coring parameters, coring accessories, and coring bit. It is critical to the project to collect the core and the added challenge of only single run required detailed workflow. Borehole size, mud wt, rate of coring and coring parameters were challenging due to the given one time opportunity. As a result, successful 100% core recovery is achieved, core retrieval to surface ensuring least core damage, this is demonstrated by CT scan which indicated no tripping out induced fractures. Well site core preservation reduced any weathering alteration, the selected stabilization method allowed minimal invasive to the core. Electrofacies guided by the whole core CT scans allowed the best coverage to the reservoir's properties. Long and large diameter plugs were achieved. Cleaning pilot study facilitated the selection of least damaging cleaning and drying method. Pilot small core analysis programs, and close follow up, and the analysis of raw data reduced the risk of unrepresentative core analysis results. Conventional core analysis data allowed refining and enhancing premeasurement electro facies and allowed a distinctive rock typing. The detailed planning permitted us to secure 100% core recovery and ensured core is reached the surface with least possible damage. The followed core analysis strategy reduced redundant experiments and allowed representative results at the same time optimized on the cost. This paper demonstrates the best practice that is followed in challenging environment of shaly sand sequences to successfully cut core and develop a program, and workflow which reflects the uncertainties to be solved.