Proposed Refracturing-Modeling Methodology in the Haynesville Shale, a US Unconventional Basin

Abstract

Summary During the downturn in the oil and gas industry, many operators have chosen to refracture their previously underperforming wells to boost economics with lower investment compared to drilling new wells. More than 100 horizontal wells have been refractured using chemical diverters across multiple basins in North America since the second half of 2013. Many papers have been published discussing these case studies. However, the refracturing results have been inconsistent. One of the biggest challenges of refracturing with chemical diverters is not knowing what is actually happening downhole. To understand what is happening better, more refracturing modeling should be performed to more reliably predict production results before spending the upfront capital for a refracturing treatment. We propose a refracturing numerical simulation methodology to take into account the historical production depletion using the calculated pressure and stress measurements along the lateral and in the reservoir. The altered stress fields resulting from reservoir depletion are calculated through a comprehensive workflow coupling simulated 3D reservoir pressure with a geomechanical finite–element model described in a previously published paper. After the stress and pressure are updated, the new approach outlined in this paper is validated by production history matching real data from a previously refractured well in the Haynesville Basin to provide greater confidence in the end results. The main uncertainty in the process is how much of the lateral was stimulated. In this paper we also provide a sensitivity example to show how the model can be altered to predict different lateral coverage percentages. Refracturing modeling still poses a major challenge for engineers because of the reservoir complexity and uncertainty downhole while refracturing (e.g., reservoir heterogeneity, isolation efficiency). However, our proposed refracturing approach provides a basic guideline on how to model refracturing treatments in a numerical simulator with the help of altered stress fields caused by reservoir depletion. This can be used to better understand why previously refractured wells perform the way they do and to better predict the performance of future refractured wells in both gas and liquid reservoirs.