Search

Routine and Special Core analysis (RCAL and SCAL) are the cornerstone of Petrophysics Modeling and Formation Evaluation. In order to obtain the required information, it is important to have quality core, its processing and analysis. This paper summarizes current practices vis-à-vis improvements made in key technical areas. Coring and core analysis are cost-intensive processes. Only quality data from representative core plugs can offset the high cost and can help to achieve the objectives of coring and core analysis. To obtain consistent quality core plugs, coring practice, on-site handling and plugging procedure have to be the best in class. Coring and core analysis in the shallow-depth Heavy Oil Fields in Northern Kuwait have been in place for some time. The processes like i) coring operation ii) on-site core handling and preservation iii) core slabbing iv) core plugging and finally v) core analysis are continually improved. In order to be efficient and cost-effective, all the above processes were re-visited, quality gaps identified and improvements implemented by incorporating unconsolidated formation characterization from the available extensive petrographic studies. For example in the coring practice front, coring and core handling protocols were modified for sour heavy oil-bearing formations noticed in parts of the fields. On-site dry ice was used in addition to the prevalent practice of normal freezing. In the laboratory analysis front, obtaining representative plugs and getting useful results from them were the key challenges. Compared to the previous practice of liquid N2 injection from top only during core slabbing by band saw, liquid N2 injection from both top and bottom resulted in improved core integrity. The previous practice of plunge cutting of plugs with liquid N2 was continued. Before any analysis, Computer Tomography (CT) scan of the plugs was performed to discriminate plug-integrity related issues. This paper discusses lessons learnt from past coring and core analysis processes and their impact on heavy oil development. Improvements to these processes as cost-effective measures are presented through real examples. Recommendations for improvement include field procedure, laboratory process, and usability of the tests performed, which may be useful to the industry where heavy oil core analysis is used.

The evaluation of the reservoir wettability is fundamental to the understanding of fluid flow in porous media. Wettability has direct impact on saturation end points and the shape of capillary pressure and relative permeability curves. This will, in turn, directly affect the relative movement of the reservoir fluids and eventually affect the displacement efficiency of oil by the different injected fluids. Having reliable wettability data deems very necessary for reliable predictions of expected oil recoveries under different development options. The Amott and the USBM tests are the most commonly used methods for quantifying reservoir wettability. Combination of the two methods is also in use. In addition to the elaborate experimental effort and time required for these methods, the USBM method does not recognize very strongly water or oil wet systems, while Amott method fails to distinguish between important degrees of strong water and oil-wetness. This paper describes a new technique, the Rise in Core (RIC), wettability characterization method based on a modified form of the Washburn equation. It enables relatively quick, accurate measurements of wettability in terms of contact angle and not wettability index as the other methods do. The method is easy to use and requires no complex equipment. During the RIC experiments, core samples saturated with one reservoir fluid are subjected to imbibitions from a second reservoir fluid. As the imbibition process takes place, the core samples weight changes continuously due to adjustments in relative saturations of the two fluids. Monitoring the square of the core mass change with time using a high precision balance, the acquired data is analyzed with modified Washburn equation to determine the cores wettability. For the sake of assurance, RIC wettability measurements were compared to ambient conditions modified Amott-USBM measurements for a thick limestone oil reservoir using core plug pairs from different heights above the free water level. The results compare well. The RIC technique proved to be much simpler to construct, much faster to perform and much easier to analyze and interpret than traditional methods. Moreover, the method gives the operator a chance to evaluate the uncertainty in the wettability data.