An Approach to Identify the Sink Holes through Seismic Imaging - A Case Study from West Kuwait Field

Abstract

Sink-hole is a closed depression (Karst feature) which drains fluid underground below. Shuaiba formation of Lower Cretaceous age is known to have Karstic topography with ubiquitous sink-holes throughout the West Kuwait area. It formed at the intersection of Joints or fault planes and solution of lime stone, underlying superficial fluvial deposits resulted gradual subsidence, forming a sink hole/ doline features. While drilling in one of the well of Dharif field, West Kuwait through one of these shallow sink-holes (unknown before drilling) to reach our targeted reservoir down below in Jurassic is a real horrendous experience. It immediately starts with severe, unprecedented and uncontrollable lost circulation (40,000 barrels of Mud) in 22’’ open hole section, causing huge loss of man days/rig days and cost. Altogether 13 cement plugs were placed. Ultimately well was controlled and reached the target. Geophysical analysis of a nearby released well of the same field was taken up. The result confirmed the presence of Sink hole/ Doline feature passing through the well and on the basis of the study, surface location and well trajectory was shifted. This paper presents an overview of efforts and methods in imaging those sink-holes in Shuaiba Formation through seismic attribute analysis and subsequent planning for new future wells bypassing these Shuaiba sink-hole features, thereby enhancing the safety of the well, efficiency, and cost effectiveness. After scouting different seismic attributes, the ESP (Event Similarity Prediction) and Curvature technique were found suitable and most appropriated in the present scenario. It is related to discontinuities/ dissimilarities observed in the seismic and were used to identify the sink-hole features. These dissimilarity measurements yield the visual identification of such features as faults, facies changes and other Geological patterns also. These Sink holes have been identified in all fields ( i.e. Minagish, Umm Gudair, Abduliya and Dharif ) of West Kuwait and discussed in this paper. Other utility of these attributes are to identify the locale of water disposable wells. In Minagish field some water disposable wells also have been planned and drilled on the basis of this analysis.