A Holistic Approach to Drill First Deep Horizontal Well with Multistage Fracking in Tight Carbonate Reservoir - A Case Study of Lower Indus Basin in Pakistan
Authors: Usmani M. Mohsin , Kamal S. 
Published: November 2017

This paper presents the modern and fit for purpose methodologies, challenges with mitigation, special consideration from geological, drilling and completions to successfully deliver first deep horizontal well with lateral length of ~1300 m and open hole multistage fracking in tight carbonate reservoir in Lower Indus Basin of Pakistan. The paper also discusses economic feasibility of making re-entries into suspended vertical wells in generally high cost services infrastructure in Pakistan. The methodologies include special deliberations on; scenario based Geomechanics Modelling, Wellbore Placement Optimization along with economic analysis by using Re-Entry versus New Well, Formation Behaviors, Drill String Design, Drill Bits Design, Hydraulics and Torque and Drag (T&D) modelling with friction factor calibration, Drilling Fluid and Strategies, Downhole Problems & Mitigations, Wellbore Quality for Open hole Multistage Fracking – All challenges, associated risks are discussed and mitigated in detail.

There were two main challenges in the wellbore placement; first is the requirement of wellbore to intersect maximum critically stressed fractures that required a new wellbore to drill and intersect but the economics of new wellbore was not feasible. Drilling team optimized the placement of the well and utilized an existing suspended wellbore to align well trajectory without compromising multistage fracking requirements. This had significantly reduced well cost and enabled the operator to proceed further. The second challenge was the wellbore failure that might have compromised hole quality and multistage open hole fracking on which the project economics based heavily. Two different fault regimes were present around the well that made the placement of wellbore more challenging. Wellbore trajectory was refined with multiple sensitivities of Geomechanics to fit the safe mud weight window. The LWD suits were run to enable the Geosteering in to sweet fractured zones. T&D model was developed and calibrated at real-time to take decisions. The drilling fluid was designed with special additives to encompass high temperature and stress caging of formation to prevent wellbore failure as well as to reduce Torque and Drag. Bit designs are also revamped that successfully drilled high UCS formations with minimal thermal cracking & favoring the RSS system to achieve landing the full lateral within top 30 m of formation. All aspects were thoroughly addressed and mitigated successfully resulting in to successful deliverables of the well project within the stipulated time and cost.

The holistic approach presented in this paper had addressed special considerations to be given to successfully deliver horizontal wells with multifracking in tight gas reservoirs in Pakistan by rerunning economic sensitivities of already suspended wells in premature tight gas fields that restrained operators to further work on development due to failure of earlier similar projects and negative economics.