Challenges in Testing and Completion of an HP/HT Reservoir in Kuwait

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 167647, ’Challenges in Testing and Completion of Highly Sour HP/HT Reservoirs in the State of Kuwait,’ by Y. Al-Salali, H. Al-Bader, V. Duggirala, M. Ayyavoo, P. Subban, A.R. Al-Ibrahim, and A. Rajkhowa, Kuwait Oil Company, prepared for the 2013 SPE Kuwait Oil and Gas Show and Conference, Mishref, Kuwait, 7-10 October. The paper has not been peer reviewed. Recently, a new structure located in northwestern Kuwait was drilled and tested with a deep-drilling rig. Formations in this deep structure have very low porosity and permeability. During short-term testing, wells produced oil and gas with, unexpectedly, the highest hydrogen sulfide (H2S) content of any reservoir so far discovered in Kuwait. Because the reservoir was rated as high-pressure/ high-temperature (HP/HT) and sour, it was a challenge to test the wells safely and successfully. Introduction Jurassic carbonate reservoirs in Kuwait fields are deep, low-permeability, and HP/HT and generally contain sour volatile oil/condensate and gas. Formations containing these deep reservoirs are tight and naturally fractured carbonates. Najmah (NJ), Sargelu (SR), Upper Marrat, Middle Marrat, and Lower Marrat are the five formations proved to hold hydrocarbon- bearing reservoirs. NJ and SR formations are tighter than the three Marrat formations. The NJ formation consists of limestone at the upper part and shale at the bottom. The SR formation consists mainly of shale and limestone. Both are naturally fractured reservoirs, so fractures play an important role in production. The Marrat formations consist mainly of limestone, occasionally with streaks of anhydrite at the top and with streaks of shale at the bottom. The core analysis of the Middle Marrat formation shows that dolomitization plays a major role for matrix-porosity enhancement, which is responsible for good reservoir character. As part of an exploration strategy, a new structure in northwestern Kuwait was drilled to deep Jurassic formations. This new structure is a northwest/southeast- trending doubly plunging anticline and is intersected by a number of longitudinal- and transverse-fault sets. Earlier, a significant discovery of light oil and gas from the new deeper structure was made from an unsuccessful Paleozoic well through re-entry. After the discovery of light oil and gas, three more exploration/delineation wells were drilled to confirm the reserves potential of this structure. Some of the wells are located near the crest of the structure, whereas some are 1.5 km from the crest (Fig. 1).