Malaysia’s First Real-Time Fiber Optic Logging with High-Fidelity Distributed Acoustic and Temperature Survey Conveyed Via Slickline: A Solution for Uncertain Downhole Integrity Condition
Authors: Shahril Shakri Shaifi , Mohd Johan Mohd Alham , Mohd Munir Dayang Nuriza Z. , Mamat Muhamad Aasif , Paul Benton , Ahmad Azhari Ahmad Hafiz , Zainal Abidin Nurbaizura , Hashim Haziq , Mahue Veronique , Pouladi Behzad , Dawson Peter 
Published: October 2022

One of the challenges for brownfield operators managing over 20 year-old wells is the uncertainties of well integrity impacting the effort to access the remaining oil in place. EnQuest known as the operator of choice for maturing and underdeveloped hydrocarbon assets, sees this challenge as an opportunity to grow by exploring the best approach in the market to meet our objective. This paper presents one of EnQuest’s wells that may have a crossflow interzone between water to the oil bearing reservoir. Well ‘Z’ is a single oil producer completed in 1997 but shut in since 2001 due to a high water cut. This well produces from three zones namely A, B and C. Zone A is expected to produce oil but well test results showed a 100% water cut. Offset well suggest the water bearing is contributed by Zone B.

The High-fidelity Distributed Acoustic and Temperature Survey (‘DAS’ and ‘DTS’) was evaluated to determine the possibility of crossflow behind the casing. The unique data solution using a combination of DAS and DTS technology based on engineered fibers, allowed for continuous and wide coverage logging of the well. Real-time data acquisition and displays of the entire wellbore led to a better understanding of the well’s dynamic and transient behavior and ultimately to a rapid and complete well integrity assessment. The abnormal fluid movement detection during shut-in was achieved through the highly sensitive sensor array, within the low acoustic frequency range, something conventional logging techniques would have missed. This service was deployed via a normal slickline unit with additional hardware required for real-time monitoring. Twelve hours of data were recorded, under a baseline shut in condition, followed by a flowing condition and then a hard shut-in. Real-time data processing and interpretation were performed onsite during logging operations by a service provider’s experts.

An unexpected result was discovered with the water contribution identified as coming from Zone B through a leaking Sliding Sleeve Door (‘SSD’) which was in a closed position, as cyclic liquid movements inside the tubing originating from Zone B and past Zone A were detected and tracked from a low frequency DAS signal. Moreover, clear acoustic activity was measured at two gas lift orifice valves during the shut-in condition; these were likely allowing the passage of the reservoir fluids into the annulus. Finally, during flowing condition, all production clearly showed that crossflow originated from Zone B to A, by both DTS and DAS measurements. This explained the water production observed at the surface. Results obtained were well received and immediate was planned action to isolate the water source resulting in 0% water produced afterwards establish movement via slow strain DAS and noise logging analysis.