Identifying Completion Problems
The same type of oil geochemistry (oil fingerprinting) data can be used to identify mechanical problems with well completions.
The mechanical problems that can be identified using oil fingerprinting include problems with the initial well construction (such as communication behind casing due to a poor cement job), as well as problems that develop in a well over time (such as tubing string leaks or casing leaks).
Tubing String Leaks
Using an excellent case study from the Gulf of Mexico, Hwang and Elsinger, (1995) illustrate the use of oil geochemistry (gas chromatography) to infer a leak in one string in a dual tubing string completion. A subsequent work over of this well confirmed the breach of the tubing string at the point suggested by the oil geochemistry. The breach evidently resulted from the omission of a blast joint that should have been installed at the point of the eventual rupture, but which had inadvertently been installed one tubing length shallower (R. J. Elsinger, personal communication to M. McCaffrey). Similar problems have been identified in other fields using the same approach. For example, Kaufman et al. (1997) applied the same oil fingerprinting techniques to identify tubing string leaks in the Greater Bergan Field, Kuwait.
Ineffective Stimulation/Fracking of a Given Interval
The geochemistry of produced fluids can be used to identify ineffective stimulation/fracking of a given interval. The same approach can be used to determine if hydraulically-induced fractures have propagated out of the formation containing a lateral wellbore and into an overlying or underlying pay zone, causing the commingling of oil produced from different reservoirs. That approach is discussed here. The same approach also can be used to identify “cross-talk” between the induced fracture networks in wells completed in adjacent formations.
Communication Behind Casing
The geochemistry of produced fluids can be used to identify communication between zones behind casing due to poor cement jobs. For example, Slentz (1981) discusses a Gulf of Mexico field which contained 10 productive horizons. After Well 31 in that filed was put on production, there was a sudden, dramatic increase in the water production from the well. Since that well was completed only in the 14,400 ft sand, the increased water production was initially assumed to be coming from that sand. However, by comparing the concentrations of various anions and cations in the Well 31 produced water with compositional data for waters known to be from other zones in the field, it was deduced that the source of the increased water in Well 31was the overlying 13,100 ft sand. Water from that interval was moving behind casing to the perforations at the 14,400 ft interval. Identifying the source of the high water cut in Well 31 provided the basis for planning a suitable work over to seal off communication behind casing and put the well back on production.
With all of these applications, the relative abundance of various compounds in the petroleum are used as natural tracers to identify completion problems by allowing produced fluids to be tied to specific reservoir intervals.
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Hwang R. J. and Elsinger R. J. (1995). Detecting production tubing leak by time resolved geochemical analysis of oils. Society of Petroleum Engineers, 355-367.
Kaufman, R. L., H. Dashti, C. S. Kabir, J. M. Pederson, M. S. Moon, R. Quttainah, and H. Al-Wael, 1997, Characterizing the greater Burgan Field: Use of geochemistry and oil fingerprinting: SPE Paper No. 37803, p. 385-394.
Slentz, L. W., 1981, Geochemistry of reservoir fluids as a unique approach to optimum reservoir management : SPE paper No.9582, p. 37-50.