Drilling of HPHT High Angle Well in a Fractured Reservoir-A Case Study

Abstract

Kuwait has been drilling and producing from the deep, sour Jurassic reservoirs during the past 30 years. Drilling high angle wells / horizontal wells can provide a means to intersect possible oil bearing fractures besides extending the drain hole length for increasing productivity. The wells drilled to these prospects are challenging because of HPHT conditions, narrow mud weight window and sour gas. The Jurassic reservoirs itself exists below a deep high pressure formation G bearing multi Salt-Anhydrite sequences. The Jurassic wells are typically based on big bore well design with the final hole size ending in 6 ½"/6" hole size. The well constructions typically comprise of seven casing policy and requires 15 K well control equipment. It is imperative that surface/intermediate casing strings are run to the maximum depths possible in order to reach well TD in the planned workable hole size. The isolation of formation G with the planned 10 ¾″ casing is essential to drill and complete the wells efficiently. In well A-14, due to complex geology, the required formation top could not be ascertained. The well construction was altered to case off the unexpected recurrent high pressure section which led to downsizing of the available hole sizes to drill upper and lower Jurassic reservoirs in slim hole. As the planned horizontal of required length was deemed infeasible in 4 ½" hole size, the well was converted to an high angle well. The unusual presence of fracture corridor with high pressure hydrocarbons below formation G posed a series of challenges. The drilling window was extremely narrow between 18.4-18.6 ppg where drilling had to be continued either with ECD or under losses with high density fluid of 18.5 ppg. The requirement to achieve the well profile with known limitation of directional drilling tools to use LCM pills was planned with due controls. On many occasions, the removal of ECD resulted in gains and many well control operations had to be resorted to including bull heading during trips. The well was drilled to TD and the upper Jurassic reservoir tested successfully. The paper will present lessons learnt, practices employed to drill with losses and gains, tripping considerations, fishing complications, slim hole drilling challenges, improvisation of drilling and cementing practices in near total loss situation and directional drilling techniques adopted. This would then provide the basis for future optimization in these types of wells.