Abstract

In unconventional reservoirs, several horizontal wells are drilled within each well pad, and could have different production profiles. Automatic history matching (AHM) is the process of inversely calibrating fracture geometry based on field production. The main challenge of AHM is to reduce the uncertainty of model parameters for multi-well history matching. This work presents an improved RWM-MCMC algorithm that is capable of characterizing fracture configurations and other properties of a well-pad with a significantly reduced computational cost for 3 wells’ calibration. The new algorithm picks the case with minimum global error from previous iterations as the first current value of the d-dimensional Markov chain, which could not guarantee this is the optimal value available for each uncertain parameter. In the new algorithm, the first current value of each uncertain parameter is chosen independently using the case with the minimum local error of the well that each uncertain parameter affects. Secondly, once the first current value of the d-dimensional Markov chain is found, we fix the current value of the whole Markov chain. An accepted proposed value is added to the set of accepted proposals, but not used as the next current value. We applied this novel algorithm to three shale gas horizontal wells in the Sichuan Basin. The results show an exceptional match between the modeling results and field observation. After 6 iterations, the new algorithm captures the presumed true solution, which reduces the computational cost by half. And the best match case matches the production profiles of all 3 wells perfectly. The proposed algorithm obtains better global optimums of model parameters with high precision and allows us to provide superior characterizations of fracture properties/geometries of multi-wells in a well pad setting, providing valuable suggestions for well spacing optimizations.

Introduction

In some parts of the world, unconventional reservoir developments are characterized as both fast-paced and volumetric, meaning pad-level drilling and production usually containing more than 2 wells. Some operators can develop roughly 100 unconventional horizontal wells per year. Given by this characteristics and background, post-frac evaluations and completion designs become crucial, thus it is detrimental for operators to ignore effectiveness quantifications of hydraulic fractures. Lots of research has been done, in an effort to understand hydraulic fractures. The main ones involve fracture propagation modelling (Wu and Olson, 2015; McClure et al., 2020) and diagnostic technologies (Sakaida et al., 2022; Leines-Artieda et al., 2022). However, further knowledge to better understand effective hydraulic fracture geometries is still required.

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