Enhanced Reservoir Contact using new LWD Technology in Thin Channel Sands

Abstract

The drilling of development wells in sand stringers involves very thin and sinuous targets. These targets are the channel sand stringers and contain a substantial amount of hydrocarbons. Optimal well placement is a requirement for these very thin reservoirs in order to drain them in a cost effective manner. Conventional well placement has met with limited success in stringers and the production can be expected to be low from these stringers. A technology driven approach of detecting the formation changes early during drilling was needed. These changes, when addressed, can be translated into maximizing reservoir contact, limiting well-bore tortuosity thus enhancing optimal production. Due to the uncertainty that is inherently present in the distribution of the channel sands, the prediction of the azimuth of channel meander can now be confidently solidified with new deep and directional electromagnetic measurements (EM) tool. This is a technology which uses directional EM through the use of tilted and transverse current-loop antennas. By detecting the upper and lower conductive shale boundaries the wells have been steered in this very challenging environment of channel sands. This technology has proven to be a major success in the development of the sand stringers by improving the Net to Gross ratio by more than 50% and hence the longevity and producabilty of the stringer wells as compared to conventional well placement LWD techniques. Introduction Fluvial channels are an important petroleum exploration target in many basins due to their high sand quality and excellent hydrocarbon trapping mechanisms. One way to achieve higher recovery factors in such reservoirs is to increase reservoir contact by drilling horizontal wells. Horizontal well placement in such an environment is challenging due to the changes in reservoir thickness and sand body orientation. To meet this challenge, it is critical to understand the shape of such bodies and the features associated with such depositional system. Flowing rivers in fluvial environments deposit sands in different ways depending on several factors such as stream gradient, consistency of discharge rate, transported sediment grain size, type of the scour surface, the effects of vegetation and natural levees. Depending on these factors we can have different types of fluvial deposits. Recent development drilling operations in Saudi Arabia involve targets near the flanks of the main structure. In last few years a number of wells have been drilled using the newly developed well placement technologies and significantly better net to gross ratio were achieved. The objective of this paper is to share the results of advance well placement process using new technology and its application in main clastic oil fields of Saudi Arabia. Geological Setting The reservoir is thick sequence of quartz-rich sand stones, siltstones, shale and various types of ironstones (siderite, chamosite, and glauconite).