Deliver the Best Production Potential of the Multilateral Well in Tight Gas Carbonate Reservoir with Underbalanced Coiled Tubing Drilling (UBCTD)
Authors: Bernadi Bondan , Al Shehhi Hajar Ali Abdulla , Abdulla Al Ameri Sara Saleh Abdulla , Alawadhi Fatima Omar , Mengal Salman Akram , Yousfi Fawad Zain , Mohamed Ihab Nabil , Al Hosani Mariam Ahmed , Al Bairaq Ahmed Mohamed 
Published: March 2023

The nature of tight gas reservoir consists of heterogeneous sub-units separated by impermeable denses and various depletion level has become the greatest challenge on how to exploit this typical reservoir at its maximum. Despite maximum reservoir contact is the best method to deliver the highest well production, this paper tries to tell another success story about UBCTD applied in a triple lateral well which can deliver greater productivity than a normal overbalanced multilateral well.

The study methodology begins with the evaluation of the current remaining potential sweetspots throughout the reservoir. The assisted history matching is used to generate 3 different model realizations: Low - Mid - High case that can map-out sweetspot distribution called Simulation Opportunity Index (SOI) map. SOI integrates 3 independent components selected from static and dynamic parameters: reservoir permeability-thickness, movable gas and reservoir pressure from a historically-matched dynamic model. One particular area is then selected and evaluated furthermore for the final new well and trajectory placement.

The well was drilled as a triple lateral with one of the lateral was fully placed in prime sub-unit that likely holds the potential remaining sweetspot in the area according to SOI method with expectation to maximize its recovery. During the drilling, UBCTD technique was implemented because it offers several advantages such as reduction of formation damage, reduction of drilling fluid loss into formation, avoiding losses-related drilling problems and risk of differential sticking and creating cost saving for completion and stimulation requirements.

Earlier study in the field signified that generally, the well productivity is strongly influenced by the type of the lateral and the geological structure. For instance, the triple lateral well located at higher structure normally gives higher productivity than the triple lateral well located underneath it. Theoretically, higher productivity will be given by the triple lateral compared to the situation if the same area is developed by dual lateral or even by the single lateral well. Currently, the implementation of UBCTD in this triple lateral well was confirmed to provide better productivity up to double exceeding a conventional overbalanced with the same well laterals. Greater initial gas production rate with high THP was evidenced during the well clean-up.

UBCTD application in tight gas reservoirs is not only aimed to improve the initial well productivity significantly beyond the conventional overbalanced well but it is also expected to create more equal pressure drawdown distribution along the lateral drain because of many given advantages as stated above. At last, cost saving can be performed because the operating cost which is usually spent on normal wells for well stimulation can be reduced.