Proper Well Control & Decision Making While Drilling: A Case Study from an Onshore Carbonate Reservoir in the UAE
Authors: Thakur Parmanand , Anwar Mohamed , Al Arfi Saif , El-Farouk Omar , Moustafa Hassan , Elkholy Mohamed , Alah Ahmed Daif 
Published: January 2016

Borehole stability while drilling in one of UAE's carbonate onshore reservoirs could be challenging due to the uncertainity of formation pressure. With such inaccurate Formation pressure, the regular action taken is to use a higher mud wight to avoid getting unexpected kick or blowout. On the other hand this high overbalance mud weight could lead to big possibility of differential sticking; it also affects the drilling performance & cause formation damage. When it comes to proper decision-making in drilling and delivering a healthy well, accurate formation pressure measurmtent is the only solution in mud weight program.

Formation pressure plays a major role in everything related to drilling and production from within a reservoir. Downhole pressure testers have long been a key component in a reservoir engineer's analysis and well planning. There are the determinations of formation pressure, fluid contacts, reservoir connectivity & near wellbore mobility. Real time applications of formation pressure while drilling are obvious in mud weight management, safe selection of casing points, caliberation of pore pressure predicitons, geosteering & obtaining data in high-risk wells.

Traditionally, Formation pressure data have been acquired using wireline formation testing different tools upon reaching section or well TD, but due to the difficulties of running wireline tools in such high angles wells, high possibility of getting stuck due to high overbalance pressure & formation pressure change from well to another, the best option was to use while drilling Formation pressure testing that provide accurate formation pressure, help in real time mud weight control decision making & save trip time needed for wireline runs. The Potential operator cost efficiencies of acquiring valid formation pressure data while drilling are becoming more influential in deciding the value proposition of a wireling reservoir characterization program.

Incorparating formation pressure testing into the drilling process presents challenges to perform measurments in highly controlled parameters like limited testing time, drilling environment noise, continuous circulation while testing to insure wellbore safety. Providing an accurate while-drilling formation pressure testing (LWD tool) allows a continuous approach to data evaluation & decision making. The ability to measure accurate LWD formation pressure data in a variety of hole sizes represents a significant opportunity for safe & costeffient wellbore construction specially in challenging environments.

A logging-while-drilling (LWD) formation tester was used in combination with a normal LWD gamma ray (GR), resistivity, density, and neutron to drill through the carbonate reservoir well. While drilling, formation pressure tester tool was recording in real-time a lot if data such as annulus pressure & equivalent circulating density (ECD) that provided a good indicator of borehole cleaning and mud conditions. In addition, different pressure stations were acquired to ascertain formation pressure and overbalance.

Results from the LWD pressure formation tester helped the drilling team make the right decision to safely drop mud weight without any risk and reduce overbalance pressure, avoiding any possibility of losses or differential sticking. Hence, reducing mud weight also increased rate of penetration (ROP) and reduced formation damage.