A Novel Fishbone Hydraulic Fracturing Technique for Tight Carbonate Reservoirs in Iraq: A Comparative Numerical Study with Traditional Stimulation Method

Tight oil reservoirs are widespread around the world and are unconventional due to their low permeability and typical composition of shale. The traditional technique of exploring these reservoirs is usually hydraulic fracturing, which has not had much success in carbonate reservoirs in Iraq. This study aims to provide an appraisal of a new method to improve oil recovery in these challenging formations, offering a detailed evaluation of its effectiveness compared to traditional stimulation techniques. We analysed and compared horizontal well, fishbone stimulation, multi-stage hydraulic fracturing, and our new proposed approach, which we call Fishbone Hydraulic Fracturing Stimulation (FHFS), using numerical reservoir simulation software. The dynamic reservoir model was constructed using real data from an Iraqi field, with a multilateral technique and local grid refinement (LGR) to simulate a single fishbone well followed by hydraulic fracturing in open-hole completion. Multiple scenarios were considered in the evaluation of the potential for this method to enhance oil recovery compared to traditional stimulation methods. Additionally, sensitivity analysis was performed on different reservoir parameters. Simulation results of a six-year period of production indicate that the FHFS technique significantly enhances cumulative oil production in a tight carbonate reservoir (the Sadi formation) compared to alternative stimulation techniques. An increment cumulative oil production of 45-50% was achieved with FHFS compared to standard Fishbone stimulation. The result was 2,8003,000% higher than a conventional horizontal well. These results are based on the FHFS enhanced of permeability from 0.65 md to 165 md for the Sadi formation. To evaluate the durability of the analysis, the fracture induced permeability improvement was adjusted to 100 md given that permeability is a critical factor in tight reservoirs. Under this condition, FHFS yielded approximately 30 % higher cumulative oil production compared to standard Fishbone Jetting Stimulation. When the permeability enhancement was reduced to 75 md, FHFS still outperformed Fishbone, but with a reduced improvement of about 20% in cumulative oil production. However, at 40 md, fishbone outperformed the FHFS, while at 45 md, both methods yield equivalent results. Therefore, given the inherent uncertainty of future oil prices, it is imperative to develop and adopt highly productive, pre-emptive techniques for tight reservoirs, which may be feasible to maximise production. The most significant finding is that FHFS significantly enhances recovery in tight formations. This is critical because higher recovery rates directly impact the economic viability of tight reservoirs. This study presents a novel systematic evaluation of FHFS, an emerging but underexplored stimulation technology. By integrating the benefit from the unique geometry of fishbone wells with traditional hydraulic fracturing, this approach offers a 45% improvement in cumulative oil production compared to existing techniques. The findings provide insights for engineers on the potential of FHFS as an innovative and highly effective stimulation method for tight carbonate reservoirs, particularly valuable during periods of high oil prices.