Using LWD Tools to Enhance Drilling Operations – A Case Study

Abstract

Drilling Exploratory and Appraisal wells can be challenging especially when faced with narrow mud weight / formation breakdown gradient windows and the potential for rapid pressure ramps. Operators engaged in the search for, and production of, hydrocarbon reserves in Tertiary basins are frequently confronted with complications associated with over pressured (abnormally high fluid pressure) formations. This is particularly the case in some of the Offshore Assets of Addax Petroleum. The problems associated with these formations are of direct concern to the combined activities of all phases of operations, which include geophysical, drilling, geological and petroleum engineering, thus the knowledge of the pressure distribution of a given area of operations would greatly reduce the magnitude of many of these complexities and in some cases, would completely eliminate them. This paper presents how the use of the Baker Hughes INTEQ "TesTrak™" tool has been used to measure formation pressures while drilling (before switching off pumps to make connections). On one exploration well, it was observed the well flowed when the pumps were switched off to make a connection, thus indicating the Equivalent Circulating Density (ECD) was providing the overbalance over the formation pressure. It is also important to note that there has been a transition in optimizing the efficiency and functionality of this tool where the the Bottom Hole Assembly (BHAs) have been re-configured with the TesTrak™ being run "upside down" so that the formation pressure measuring probe would be closer to the bit and thus enable the earliest possible formation pressure information, minimizing the likelihood of a pumps off event. The process of automatic cycling of the pumps, which was required to toggle the tool back to drilling mode was minimized (only with full knowledge and agreement of all involved in drilling operations), after it was observed how dangerous it can be loosing the the over-balanced supplied by ECD. To maximize the advantage of having the logging tool read formation pressures real time, the TesTrak™ has been used to take formation pressures to verify prognosed pressure transition zones such that the mud weight can be adjusted to suit the actual pore pressure measured.The TesTrak™ tool is presently also being used by Addax Petroleum for data gathering while drilling development wells eliminating the need to run wire-line or pipe conveyed logging in highly deviated and horizontal wells. This has saved rig time and drilling operations costs in addition to enhancing drilling efficiency. It has also improved well-site safety, helped optimize decision making and decreased the risk of differential sticking.