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. Abstract 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. Introduction 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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TX 75083-3836, U.S.A., fax +1-972-952-9435. AbstractEffective matrix acid stimulation is one of the keys to maximizing and maintaining long-term North Field well productivity. ExxonMobil and RasGas Company Limited (RasGas) had jointly developed an integrated methodology to optimize matrix stimulation for layered Khuff reservoirs, specifically for K1-K3 and K4 completions. The integrated methodology is a continuous process which consists of five main elements to help overcome the well and reservoir challenges, including reservoir objectives, completion strategy, stimulation design, implementation, and evaluation. 1 Success of K1-K3 and K4 completions led to high expectations for K1-K4 completions required for the recent development expansion. However, the much longer K1-K4 producing interval substantially increased the challenges such that existing stimulation tools and methods were no longer sufficient to achieve the aggressive stimulation targets desired for these wells.Initially, retrievable mechanical isolation plugs were developed and qualified for use to achieve effective stimulation using already proven methods for K4 completions and K1-K3 completions. Due to the increased operational risk associated with mechanical isolation techniques, development of alternative methods and extension of existing methods were necessary. Multiple parallel paths were taken to investigate all aspects of well stimulation, including perforating techniques, diversion, number of stimulation treatments, stimulation vessel capabilities, and well / reservoir productivity. Field trials were conducted for selected technologies, and additional data were collected prior to, during, and after the stimulation treatments. Additionally, a process and associated tools to quantitatively evaluate completion and stimulation options in terms of both initial and long-term production performance were developed. Consequently, stimulation decisions could be made based on reservoir performance metrics balanced with the risks and costs associated with each option.To evaluate well performance and optimize the stimulation strategy for future wells, an advanced post-stimulation analysis methodology incorporating stimulation predictions, sequential flow data, flowback samples, and production logs has been developed. Results of the analyses suggest stimulation performance comparable to stimulation with plugs, at a greatly reduced completion cost and substantial risk reduction and time savings. Additionally, stimulation strategy optimizations were possible such that the number of stimulation treatments could be reduced for most wells without compromising stimulation effectiveness or predicted long-term performance.This paper discusses the development and implementation of alternative strategies and designs to effectively stimulate K1-K4 completions without the risk associated with mechanical plugs. Two case histories will be presented to illustrate application of the enhanced methodology. IntroductionCompletions are the critical component of a well that con...

Recent advances in multi-stage stimulation technologies, including open- and cased-hole types, have largely overlooked the advantages of single-zone stimulation due to hardware and cost limitations. In most conventional methods, multiple perf clusters are treated at once using one single frac stage with the expectation that equally-stimulated fractures will be created at each perf cluster within tens and hundreds of feet. This creates over-stimulation in some perf clusters and under-stimulation in others, which unveils the current economic and practical limits of effectively creating fractures where needed, not where it is possible to place them. Other methods use a large number of frac plugs which require additional wireline trips and later need to be drilled out, increasing the total cost and mechanical risk of the completion. As lateral length increases, many operators also face the challenge of not being able to remove all frac plugs due to coiled-tubing depth limitations. This paper introduces the recent implementation of Just-In-Time Perforating (JITP) in shale gas, unconventional plays. JITP is one of the Multi-Zone Stimulation Technologies (MZST) developed and patented by ExxonMobil over a decade ago and extensively used in vertical and S-shaped wells in the Piceance basin, Colorado, and recently implemented in the XTO Fayetteville Shale, Arkansas. JITP creates multiple single-zone fracture stimulations on a single wireline run using ball-sealer diversion and perforating guns that remain downhole during fracturing. Other key features of this method are the use of less horse power, significant reduction in the number of frac plugs, fewer wireline runs, and added flexibility in water management. This paper describes the technical advantages and business justification for applying JITP in unconventional resources and also provides preliminary results from the performance of the JITP field trials in horizontal wells.