Abstract
Abstract
Challenging formations offer most of the evident drilling problems including lost circulation, stuck pipe events resulting in financial and timeline setbacks globally. Moreover, further complexities related to loss/gain make operators revise their casing plans, wellbore trajectories along with revised engineering studies. By providing optimized drilling tactics to address issues with loss/gain and mechanical/chemical instability, unconventional technologies are available to address these difficulties and meet deadlines. Owing to inherent lost circulation, influx and stuck pipe risks in Kirthar Belt in Sindh Pakistan, the operator had to spot various loss circulation material (LCM) pills along with facing various stuck-pipe incidents in most of the offset wells, resulting in the revision of the casing program. The simultaneous presence of loss prone limestones and unstable shale make the surface sections more challenging to drill. This study assesses the use of air/foam drilling to penetrate the fractured Kirthar and Laki limestone, offering lost circulation and the chemically and mechanically unstable Ghazij shale, offering wellbore stability and stuck-pipe risks. The study also shows the management of water influx from the Kirthar formation, reducing its impact on Ghazij shale which swells in the presence of an aquatic medium. To overcome these challenges, an efficient design of compressible, multiphase foam system was designed along with the different base fluids utilized for the drilling.
Presence of water influx always limits the effectiveness of chemical inhibition properties of drilling fluid. It was critical to design multiphase fluid offering low bottom hole equivalent circulating density (ECDs) as well as maintaining proper foam quality to ensure hole cleaning in presence of water influx offered by the aquifer in the Kirthar limestone. This paper evaluates the optimal design of foam system while utilizing spud mud as well as silicate mud while drilling across lost-prone Kirthar and unstable Ghazij respectively. Moreover, chemical studies were conducted providing good foam texture under water influx to counter wellbore stability issues. Air/foam drilling offered ECD less than 2 ppg by utilizing the base fluid of mud weight equivalent to 8.7 ppg.
Air/Foam drilling enabled the operator to drill throughout without spotting LCMs or cement plugs and proceeding with the pre-decided casing program, resulting in saving 42% of the section allocated time. Whereas excellent hole cleaning was achieved without swelling of shale owing to effective management of water influx. An analysis is provided with respect to management of 16 barrels per hour (BPH) of influx with foam system. A statistical comparison between rate of penetration (ROPs) while utilizing conventional mud and air/foam system shows an increment of ROPs by 35% while utilizing air/foam system. To put it in the nutshell, air/foam drilling proved to be vital tool to drill the lost-prone and mechanically/chemically unstable formations in presence of water influx. This paper focuses on engineered study of the design of multi-phase foam system along with the onsite execution for future prospect applications as well.