The Sleeping Giant Awakens

From the editors of BARNETT: TECHNOLOGY The ‘Sleeping Giant’ Awakens For more than 20 years, many scoffed at ‘Mitchell’s Folly’ as the intrepid wildcatter doggedly probed the inhospitable shale in the Fort Worth Basin — not anymore. By Dick Ghiselin Contributing Editor Dawn lights the ailed as the largest unconventional gas play on challenges to be tackled in the Barnett. But no one Barnett, and the Hthe North American continent, the Barnett likes challenges better than the technology providers silence is shattered Shale was the harbinger of untold energy produc- in the service sector. They have applied their con- by dozens of pump tion that has spread across the US and Canada like siderable experience and learnings gained from the engines as they roar wildfire. Names like Horn River, Haynesville, Mar- activities of Mitchell and other early believers to into life, waking the cellus, and Fayetteville were all but unheard of a develop better technology that improves recovery sleeping giant. decade ago until George Mitchell proved the possi- factors, enhances reservoir contact, and reduces well Photo courtesy of bility of producing commercial volumes of natural construction costs. Schlumberger gas from the giant shale that today spans 21 coun- ties of North Texas. Variable reservoirs present With predicted peak production pegged at 8 variable challenges Bcf/d sometime around 2018, there’s still a lot of gas In shale plays, the traditional fracturing technique to be found and produced, and an equal amount of can be characterized as “perforate, pump, and pray.” December 2009 | www.hartenergy.com BARNETT: TECHNOLOGY This reasoning seemed logical as many shale for- lenging tight gas shales. “TRA helps to maximize mations and traditional logs in shales lack charac- recovery through expanded knowledge of vertical ter; however, one thing has become evident — not all and lateral reservoir heterogeneity, reservoir quality, shales are created equal, and not all sections of a lat- completion quality, fracture containment, fluid sen- eral can be treated equally. With the massive geo- sitivity, and retention of fracture conductivity. graphical extent of the Barnett Shale, it is not surprising to see differences in reservoir character- Finding the sweet spots is key istics from one part to another and differences in Like most shale play participants, Schlumberger production from one well to another. In fact, it is recognizes that knowledge is power. Finding the also not surprising to learn that different fracturing gas and understanding how to recover it requires an stages in the same well behave differently. Schlum- integrated well evaluation process that draws on berger has developed the tools and expertise to the experience of the company in gas shale devel- understand this variability. opment and its extensive suite of proven tools. The “Schlumberger has a more than 20-year history ECS* Elemental Capture Spectroscopy tool is a geo- of experience in the Barnett, and there has been chemical tool that is the basis for resource evalua- quite an evolution of technology in that time tion. This tool classifies the types of rock in the period,” said Shane Smith, Schlumberger techni- reservoir and quantifies gas in place. The Sonic cal sales manager for the Dallas-Ft. Worth area. Scanner* tool offers a better understanding of the “The first wells were all vertical, but now by far the distribution of stress and stress anisotropy along a majority of wells are horizontal because of the abil- well bore. Lastly, the FMI* Fullbore Formation ity to contact more of the reservoir. To assist with MicroImager device is used to determine the resis- the interpretation of all the data collected in this 20- tivity and clay content along the well bore as well as year span, we opened a Regional Technology Center classify the natural and drilling induced fractures in Dallas in 2007, which focuses specifically on present. These tools are used to characterize the understanding shale gas. localized stress regime (called “states of stress”) that “Completion technology has kept pace with the governs fracture propagation in shales. This infor- evolution to more horizontal completions. There mation can be used to determine the best places to has been a parallel evolution as well in fracture land new laterals, optimize perforation and staging design. We base our designs on data acquisition strategy to contact more reservoir, and avoid poten- and proper use of the data to impact the formation. tial trouble portions of the reservoir that may lead The key to unlocking the full potential of shales is to undesired fracture results. All of these things reservoir characterization and operating efficiency. help create better fracs and better production. Schlumberger has expertise in both.” Following are a few technologies and services Keeping the frac contained that have significantly improved operators’ ability to As explained in SPE Paper 124147, one of the contact more of the right rock. biggest challenges Barnett operators face when expanding their drilling activity to non-core areas is Understanding goes back to ground truth keeping their frac contained. Excessive height Core analysis performed by the Schlumberger geo- growth can introduce inefficiencies, driving up costs technical team at TerraTEK has been fundamental as well as reducing production and recovery. “You to gaining insights into the Barnett Shale. “We have can place and land your well in the sweet spots, but acquired and analyzed thousands of core samples if you don’t have fracture containment, you still using tight rock analysis (TRA) to develop a clearer may have water production issues,” said John understanding of the geology, petrophysics, and Daniels, hydraulic fracture placement optimization geomechanics affecting the reservoir,” said Smith. product champion for Schlumberger. Predicting TRA provides a detailed core measurement of rock fracture containment, therefore, is a must, and the permeability, porosity, and fluid saturation in chal- company has developed a three-step technique www.UGcenter.com | December 2009 BARNETT: TECHNOLOGY Modular Dynamic for multistage frac jobs. To prove the point, a Tester (MDT) tool client used this technique to choose a new land- configured for in situ ing point and determine perforations and staging stress testing. Image for a well drilled in an area plagued with fracture courtesy of containment issues and subsequent water pro- Schlumberger duction. StimMAP Live* hydraulic fracture map- ping was used to monitor this treatment in real time. Both the microseismic data and production information confirmed that the fracture stayed contained in the Barnett. This level of multi-measurement integration within a 3-D earth model illustrates the opportunity for step changes in shale gas development. Microseismic to simulation Daniels acknowledged that the Barnett offers lots of stimulation challenges. “Our expertise has been greatly enhanced by our ability to acquire relevant microseismic data and use it to drill and stimulate better wells for our cus- tomers,” he said. “The value of having an integrated solution is three-fold. Firstly, microseismic imaging designed to place and orient fracture perforations in has allowed us to optimize our fracture treatments, the best position every time. Key to this claim was literally on-the-fly, based on our real-time interpre- the development of the in situ stress testing tool, tations. With advanced processing algorithms deliv- which is a creative reverse-application of one of the ering results every 15 seconds, we can use this data company’s most reliable services, the MDT* mod- to help us understand when to deploy diverters or ular formation dynamics tester. alter our pumping schedule to achieve the cus- At the core of the technique is the MDT Pump- tomer’s objectives. Secondly, the integration of this Out Module, which is used to initiate a mini-frac data back into an earth model helps us truly under- while acquiring vital pressure measurements and stand the relationship between geomechanical and transmitting them to surface in real time. Here’s geophysical properties of the reservoir and hydraulic how it works: fracture placement. Lastly, the microseismic data The pump-out module is installed between two can be used to simulate production and recovery packer modules creating a very accurate mini-frac from the well using all of the data contained in the tool. The tool is positioned and mini-frac conducted 3-D earth model. At the end of the day, this infor- opposite a zone of interest identified by the ECS, mation improves our ability to manage the asset and Sonic Scanner, and FMI. The stress required to enhance recovery.” break down the formation is measured by the MDT and is used to calibrate the logs’ measurements as Horizontal re-fracs grow in popularity well as core measurements. These calibrated stress Based on information from SPE Paper 119636, measurements can then be fed back into models, Daniels offers the following: “Recently, we’ve seen allowing operators to land their laterals in the right a lot of Barnett Shale production logs that share a place as well as choose where and how to complete common trend. Of the perforation clusters in a their wells for maximum reservoir contact. typical horizontal, less than half are contributing The application of the three-step process takes to production. A few perforation clusters in each the guesswork out of picking perforation zones well deliver a majority of the gas. Both produc- December 2009 | www.hartenergy.com BARNETT: TECHNOLOGY tion logs and microseismic Microseismic events data have clearly shown that we while refracturing are not effectively contacting a Barnett Shale the reservoir. horizontal well. MS “We’ve learned that there is a events were detected lot of gas left to be produced before (yellow) and from the Barnett. So much so, after fiber diversion in fact, that we have identified cycles (blue and red). more than 8,000 Barnett wells The aggressive diver- that could benefit from re-treat- sion cycle (red) suc- ment.

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