Understanding Wormholes in Carbonates: Unprecedented Experimental Scale and 3D Visualization
- Darren McDuff (ExxonMobil Upstream Research Company) | Shalawn Jackson (ExxonMobil Upstream Research Company) | Chris Shuchart (ExxonMobil Upstream Research Company) | Dieter Postl (ExxonMobil Upstream Research Company)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- October 2010
- Document Type
- Journal Paper
- 78 - 81
- 2010. Society of Petroleum Engineers
- 4.3.4 Scale, 5.5.2 Core Analysis, 3.2.8 Well Performance Modeling and Tubular Optimization, 2 Well Completion, 1.8 Formation Damage, 1.6.10 Coring, Fishing, 5.8.7 Carbonate Reservoir, 2.1.1 Perforating, 3.2.4 Acidising
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Technology Today Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering.
Matrix acidizing experiments combined with visualization techniques commonly are used to study the details of wormhole networks formed during matrix acidizing of carbonate reservoir rock. Previous experimental studies of wormhole growth focused mainly on small linear core plugs, with only a limited number of radial-flow studies published in the literature. Results from these conventional experiments provided extensive information on linear 1D wormhole growth along with some basic insights into 2D radial growth mechanisms. However, larger-scale test systems must be considered if 3D wormhole characteristics are to be understood. Toward that end, a new method was developed that integrates acidizing experiments on carbonate rock samples up to 14 ft3 in volume, high-resolution nondestructive imaging and analysis, and computational modeling to extend the results of experiments to field applications. This article highlights the experimental and imaging components.
Substantial hydrocarbon volumes have been and will continue to be produced from carbonate formations, which hold nearly half of the world's reserves. Because these formations are highly soluble in acid, matrix acid stimulation provides a cost-effective means to enhance well productivity. Effective acid stimulation can be critical to achieving the desired longterm production rates from targeted reservoir layers.
Interaction of acids with carbonate rock has been studied extensively using quarried, outcrop, and formation core samples. Linear flow tests on core plugs are conducted to determine the optimum conditions to generate wormholes (i.e., highly conductive flow channels that connect the nearwell region to the completion). At a given temperature, the ability of a particular acid to generate wormholes is largely dependent on the acid injection rate or "acid flux,?? as illustrated in Fig. 1. The figure shows an example of a "wormhole efficiency curve?? developed for core plugs of quarried limestone. As the curve indicates, there is a certain optimal acid flux for which wormholes will most efficiently propagate along the main axis of the core plug.
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