Innovative Method To Detect Oil Water Contact And To Control Acid Placement During The Stimulation Of Wells With High Water Cut
- Mesaad Harbi (Saudi Aramco) | Rifat Said (Saudi Aramco) | Ibrahim H. Al-arnaout (Saudi Aramco) | Surajit Haldar (Saudi Aramco) | Fehead Al-Subaie (Saudi Aramco) | Christopher Neil Jenkins (Saudi Aramco) | Anton Burov (Schlumberger) | Wassim Kharrat (Schlumberger Middle East SA) | Danish Ahmed (Heriot Watt University)
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Oil and Gas Show and Conference, 25-28 September, Manama, Bahrain
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.2 Separation and Treating, 1.8 Formation Damage, 5.6.11 Reservoir monitoring with permanent sensors, 5.6.1 Open hole/cased hole log analysis, 1.6.1 Drilling Operation Management, 4.2.3 Materials and Corrosion, 3.2.4 Acidising, 3.3.1 Production Logging, 5.8.7 Carbonate Reservoir, 5.9.2 Geothermal Resources, 3.3 Well & Reservoir Surveillance and Monitoring, 2.2.2 Perforating, 1.10 Drilling Equipment, 2 Well Completion, 5.2 Reservoir Fluid Dynamics
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Water production is a serious challenge when stimulating wells in mature reservoirs. Production results after acidizing sometimes reveal a higher water cut; in some cases this change is significant enough that the well is no longer able to flow unassisted. A typical acid stimulation in the field follows a predetermined pumping schedule, where diverter is squeezed into the high water cut interval prior to injecting acid into oil zones. The diverter volume is based on a rule of thumb and the acid is pumped after assuming that the diverter is efficiently sealing the high water cut zone. Several coiled tubing (CT) matrix stimulation jobs have yielded production results of 100% water cut.
Prior to stimulation (a period of months or years), diagnostic logs were conducted to identify water producing intervals. Although, in some cases, the post-stimulation water cut may be as high as or higher than the water cut prior to the stimulation, suggesting that the diverter volume was not enough to seal the water zone. An innovative method is needed to confirm the isolation of high water cut zones before pumping acid, which would lead to increased oil production and reduce the risk of unintentionally stimulating water producing zones.
This paper shares a case history of a cased and perforated vertical oil well from a field in which the operator was able to reduce the risk of acidizing a high water cut interval through the innovative use of a fiber optic enabled coiled tubing (FOECT) string and a pressure-temperature casing collar locator real-time downhole measurement tool.
The distributed temperature surveys (DTSs) recorded with the fiber optic cable were used as an innovative method to identify the water producing zone. This method correlated with the water producing interval identified by a wireline log run some period prior to the CT job.
DTS allows the assessment of diverter efficiency and the tracking of fluids placement. In this case study, acid was confirmed to have been squeezed only in the upper oil zone. As a result, the well production increased significantly without any increase in the water cut.
The acid stimulation of oil wells becomes a challenging task when water invasion occurs in lower producing intervals. Effective acidizing of wet wells requires a temporary or permanent isolation of the water zones before pumping any acid. Failure in this critical step will lead to an increase in water cut, and most likely a failure of the stimulation. To properly perform the isolation and ensure that acid will be squeezed only into the oil producing intervals, the following steps must be followed:
1. Identify the water producing zone.
2. Isolate the water producing zone either temporarily or permanently.
3. Confirm the efficiency of the isolation before pumping acid.
4. Confirm the stimulation fluid placement zones and efficiency of the isolation after pumping acid.
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