Evaluating the Performance of Fishbone Stimulation Technology in Tight Formations: A Comparative Numerical Study of Jetting vs Drilling in the Sadi Reservoir in Iraq

Abstract Fishbone stimulation technology is an attractive stimulation method for use in tight reservoirs which consists of two types: jetting and drilling. While pervious research is mostly focused on the fundamental technical difference between the two methods, in this study we will focus on the difference between them in terms of hydrocarbon production rate as well as the impact of the number of subs on oil production rate. Fishbone stimulation wells have smaller lateral branches called "subs". Each sub has three or four needles (or ribs) that are half an inch wide and 40 feet long. Numerical reservoir simulation models were utilized using local grid refinement and multilateral techniques for simulating both methods of jetting and drilling to predict the cumulative oil produced by using real data available for an oil field in the Sadi formation in Iraq. Additionally, an optimization study was carried out for the number ‘subs,’ each comprising 3 needles (or ribs) in the case of using the drilling method and four needles in the case of the jetting method. A base case of cumulative oil production rate from the Fishbone well jetting, which consisted of 20 subs for each sub-three needle, was 189,482 m3. This aligns with an average produced from Sadi formation. The number of needles was changed from four to three (fishbone well drilling); the cumulative oil production rate decreased by 0.32%, resulting in a marginal proportional reduction in output. This indicates that decreasing the number of needles per sub led to a marginal decline in production efficiency. We reduced the number of subs to 10 and increased it to 30 and 40 subs. The simulation results showed that this modification did not affect the production difference between jetting and drilling, as the percentage difference remained within the range of 0.30% to 0.32%. However, it was observed that production increased by increasing the number of subs and vice versa. Simulation results from the Sadi reservoir showed no significant difference between jetting and drilling in the cumulative oil production rate for the 6 years that we simulated. Overall, the type of completion remained mainly dependent on the type of formation. When working with hydrocarbon reservoirs, it is best to use jetting which is preferred with a temperature limit from 150 – 160°F to control the chemical reaction that occurs when utilize 15% of hydraulic acid on carbonate rocks. While fishbone drilling stimulation has been effectively implemented in sandstone reservoirs and more consolidated formations to increase reservoir contact and enhance hydrocarbon recovery. This is the first study to compare two types of fishbone stimulation in a tight reservoir. The insights are therefore valuable for discerning the preferred completion method for hydrocarbon recovery in tight reservoirs. The findings of this study can allow engineers to choose a method not merely based off the production rate (since the two methods are close in terms of production) but also considering factors such as: cost and types of reservoirs.