Abstract

A super deep well was drilled in 1999–2000 to test the Pre- Khuff and Jurassic formations of Unayzah, Marrat and Najmah-Sargelu. The Unayzah formation had never been tested in North Kuwait before, therefore meticulous planning was required to successfully test this unknown HP-HT formation. The objective of the test was to obtain fluid samples, flow to surface and measure flow rates and establish basic formation properties to determine commercial viability from the deep formations of North Kuwait. This was the deepest well drilled in that area to the depth of more than 20,000 ft, having a formation pressure of 16,158 psi and log temp. of 350 DegF. The well was drilled with 19.6 ppg oil base mud, which was consistent with the formation pressure.

Since the well was rated as one of the deepest well in the Middle East, and it was new experience to KOC to deal with such type of wells, it was a challenging task for the management to successfully test this well. The complications in the drilling also generated lot of constraints, which were to be taken into consideration while designing the test. More than 10 months of careful planning and preparation for special equipment lead to the successful testing of the deepest formation. Special care was taken to take into account the HSE issues to eliminate any chance of loss of life or property, without compromising the test objectives. This case study details the complete sequence of planning and preparation for designing and testing a super deep well like this one, which might be referred as a bench mark for HP-HT testing of deep wells in Kuwait and other places.

Introduction

This deepest well in North Kuwait is located outside the North west corner of Raudhatain field. The well was originally planned for testing the Jurassic formations of Marrat and Najmah Sargelu. But later on, it was decided to deepen the well to pre-Khuff formation. The well was drilled to a Total Depth of 20,234', but due to drilling complications, the well was sidetracked from 19,831' and then drilled to 19,947' MD.

A 5–1/2" Liner was set in this part with shoe at 19,928' with top at 15,970'. Later on, when the well data was analyzed, it was felt that the production casings of 7–3/4" and 10–3/4" were not rated for high pressures expected from the Pre-Khuff Unayzah formation. This formation, Unayzah, was the target formation for this well which was supposed to have HP-HT sour gas.

At this point, the rig was released on 6th March 2000.

Since such high pressures and temperatures were never encountered in Kuwait, it was decided to give maximum importance to the testing of this well so that the well can be tested in the most safe and successful manner. Other than HP-HT condition of the well, there were many other issues which called for exhaustive planning, for example there were many constrains like small size of the liner, lower pressure rating of casings, non-availability of HP-HT testing equipment and expertise, likely hood of H2S presence in the gas, rig capacity etc. To address these issues, the KOC management constituted a Test team whose responsibility was to plan, procure and execute the testing operation of this well.

The Testing Team was a multidisciplinary team, which constituted experienced people and IOC secondees from various departments like Field Development, Exploration, Drilling, Field operations and Well Surveillance. There were also representatives from the contractor companies for networking with their counterparts around the world and for sharing their experience with the KOC engineers. The team had more than 20 members.

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