Analysis and numerical modelling of wireline pressure tests in thin-bedded turbidites

Abstract

This paper presents new insights in modelling wireline transient pressure tests in thin-bedded turbidites (TBTs). Permeability heterogeneities are classically evaluated from core measurements and through geological description of the reservoir, then possibly refined by simulation and history matching. Wireline formation testing (WFT) is shown to offer the possibility to obtain these details at an intermediate scale, readily available for input in flow simulators. This is critical in complicated multilayered, thin-bedded reservoir, which cannot be adequately described with conventional, logs, cores and well tests. Numerically simulated pressure responses from straddle packer tests, modelled using image logs, are matched with measured ones and the method enables the determination of permeabilities of the straddled layers. Simulation is required as no analytical solution exists for direct transient pressure analysis in these layered systems. A real case illustrates the methodology used, and we show that in such deep marine environments possible lateral geological variations are deduced from transient pressure analysis, such as sand pinching out or lensing, which could not be inferred from other static measurements. We highlight through this example and sensitivity simulations of geological effects that this technique offers an economical alternative to more traditional coring or well testing. We also discuss the potential pitfalls associated with poor acquisition designs, short test duration and the nonuniqueness of the inversion problems.