This paper describes advances in an integrated analysis workflow of Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) for water injection profiling on a horizontal well, completed with Limited Entry Liners (LEL). The well is completed as an injector with Limited Entry Liner (LEL), MRC horizontal lateral made of 18 separated zones with packers, each with variable numbers of holes. DAS and DTS data were acquired on coiled tubing, over an acid stimulation period followed by a water injection period. Previous analysis of the dataset, SPE-203065, focused on DTS warm-back models and highlighted challenges in the process; the use of the DAS data was limited. Recent re-processing of the data using advanced acoustic signal processing techniques was performed to extract several flow characteristics. Both transient and steady state injection conditions were analyzed: High-definition low frequency slow strain DAS was extracted over the shut-in to injection transient to compute an initial injection velocity profile as well as a stage level injection distribution across the liners. During steady state flow, acoustic denoising algorithms were applied to the DAS data in order to generate a spectral noise log of high signal to noise ratio (SNR) for the detection of all major injection points. Video animations were generated of spectral noise logs over time, to evaluate the dynamic behavior of the injection profile from start to end. The warm-back DTS data was analyzed for a qualitative assessment of the injection Finally, a quantitative injection profile was computed, and the results were compared against a separate PLT log at both stage and nozzle levels. The results of the transient and steady state flow analysis converged and showed the highest water intake to occur over the heel-ward stages. The depths of highest rate of change in injection velocity, aligned with the strongest acoustic signals from the enhanced noise log. Inversely, the weaker acoustic outflow activities over the middle and toe sections aligned with the smaller velocity changes. The video animations showed a stable injection profile over time. The qualitative DTS analysis confirmed the overall DAS-based injection profile. The comparison with the PLT injection allocation highlighted clear differences in the profiles. These are being discussed, as well as the possible causes for the discrepancies. This analysis demonstrates the strength of an integrated DAS and DTS analysis workflow using both transient and steady state conditions. DAS array processing techniques enabled the extraction of high-definition transient thermal plumes, allowing for an early injection profile, which was further strengthened by high SNR spectral noise logging.
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.
This paper presents the results obtained from the application of high-fidelity distributed measurements and station logs for well integrity assessment in a gas producer. Historical well data suggested the presence of sustained annular pressures attributed to the migration of gas across a leak point on the tubing. The primary objective of this survey was the assessment of the upper completion interval to identify potential leak sources and investigate any defect on the casing and tubing. A joint well integrity survey was done via a retrievable, hybrid fibre-optic sensing-based service deployed through the tubing together with a Multi-Finger Caliper (MFC) and Electro-Magnetic Defectoscope (EMDS) to evaluate the tubing profile and integrity of the Wireline Entry Guide. Given its adaptability to third-party wireline and electromechanical tools, the hybrid fibre optic cable was deployed in the well, alongside the MFC and EMDS, with zero interference effects. Real-time data analytics were performed onsite, thus informing key decisions during the survey. The leak detection program originally designed for this survey included two main monitoring periods; the baseline period to serve as a reference and a period of annular venting to create a higher-pressure differential across the tubing to stimulate the leak. However, shortly after the well was shut-in, there was a sharp decline in the annulus pressure, even before the annular wing valve was opened. A decision was made to cancel the annular bleed-off, as zero psi was recorded. Acoustic signals detected across the tubing during this period were related to cable and fluid movement during well stabilization. This conclusion was further corroborated by the MFC and EMDS log as the tubing section was found to be in a relatively good condition from top to bottom with very light corrosion across all joint (within the maximum penetration range from 0% to 30%). The Wireline Entry Guide was also found to be in a good condition without any significant damage and visible vertical crack. The temperature and acoustic responses detected across the reservoir interval were, however, indicative of ongoing crossflow during the shut-in period. It appeared that the middle reservoir zone was acting as a source, dumping gas into the bottom zone. The unique data solution provided by the fibre-optic sensing technology allowed for continuous and wide coverage logging of the well. Real-time data displays of the entire wellbore, together with the point sensor measurements, led to a more comprehensive well diagnostics outcome.
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