Matador, a guar variety jointly owned by Texas Tech University and Halliburton, is grown as a breeders' seed increase (i.e., to increase the amount of seed available) at the Texas Tech campus farm at Lubbock, Texas. Guar is a modest-looking shrubby plant. Primarily grown in India and Pakistan, it is known there as a “poor-man’s crop,” according to Calvin Trostle, associate professor and extension agronomist, Texas A&M AgriLife Research & Extension Center in Lubbock, Texas. This stepchild crop has risen in importance during the last few years as the source of an important ingredient that makes high-viscosity (as opposed to slickwater) hydraulic fracturing as effective and cost-effective a process as it is. This ingredient is known as guar gum. Made from the endosperm of the guar seed, which is ground into a fine powder, a tiny concentration of guar gum interacts quickly with hydraulic fracturing water to thicken it. In simple terms, guar gum renders the water viscous and thus capable of evenly suspending and carrying proppant deep into the fractures that are created with the enormous pressures of the pumped water. Its biopolymeric viscosity properties also help reduce friction and augment water pressure. No guar substitute has yet been developed that is as effective for high-viscosity hydraulic fracturing, although Halliburton, Baker Hughes, Schlumberger, FTS International, or their affiliates, as well as the chemical company Dupont, are working on developing synthetic polymers whose properties might rival those of guar gum. According to Mickey Callanan, president of PfP Technology, “Guar is a perfect material for hydraulic fracturing.” He cites the following elements that guar gum brings to bear: Available in large amounts Availability currently not limited Affordable, low cost Superior thickening agent Excellent friction reducer Crosslinkable Breakable Biodegradable Trostle says reported oilfield services industry numbers suggest that an average amount of guar gum required to hydraulically fracture one well could be as much as 20,000 lb. That is the equivalent of about 100 acres of average-yielding west Texas dry-land guar production (at 750 lb/acre). Guar gum is also used as an ingredient in drilling fluids and enhanced-oil-recovery methods, though not as consistently or in such vast quantities as for hydraulic fracturing. Arguably, without guar, shale gas and oil development would not be burgeoning nearly to the extent it is. Humble Beginnings to Today’s Prominence Although guar pods (with the seeds inside them), which grow in clusters on the plant, are used for human consumption, the traditional use of guar has been for cattle feed. In fact, according to Sudhir Merchant, chairman and chief executive officer of Encore Natural Polymers of Ahmedabad, India, in India “gaw – har” means “cattle – food.”

Editor's column JPT publishes summaries of 144 technical papers a year, choosing from among more than 4,000 papers to ensure that it is publishing the “best of the best.” Although this has been standard practice for the magazine for years, many SPE members, as well as nonmembers, are unclear how these papers are selected. It starts with dedicated volunteers. The JPT Editorial Committee comprises 47 oil and gas industry professionals who are experts in their field. Committee members volunteer their time to review technical papers and abstracts that have been presented at SPE conferences as well as the multisociety Offshore Technology Conference, Unconventional Resources Technology Conference, and International Petroleum Technology Conference and identify the most relevant, high-interest, and practical papers for publication. Occasionally, papers that have not been presented at a conference but submitted directly to JPT are reviewed. Reviewers also attempt to ensure that the papers represent the industry’s geographic and corporate diversity. JPT staff then summarize the chosen papers in 2–3 pages with access to the full-length paper available online. SPE members can access the full-length papers for free for 2 months at www.spe.org/jpt. Over the course of the year, JPT will publish summaries of 12–16 papers monthly in a variety of upstream areas such as hydraulic fracturing, formation evaluation, completions, and enhanced oil recovery to name a few. The committee members have diverse positions in the industry as well as backgrounds. They include professionals at operators, service companies, national oil companies, independents, consultancies, and in academia. Qualifications to serve on the committee include SPE membership, be a recognized industry expert on a particular technical topic, have at least 10 years of experience in the oil and gas industry, and have been an author of SPE technical papers. The chair of the committee serves a 3-year term as do the committee members. Current members of the committee and their job affiliations can be found to the right of this column. The goal of publishing these technical paper summaries is to provide readers with short versions of important papers. In years past, JPT published full-length technical papers but that allowed for publication of only a few over the course of the year. Publishing summaries allows readers to be exposed to a variety of ideas and technology applications and an avenue to easily access the full-length paper if interested. This help meets JPT ’s, and SPE’s, goal of disseminating and sharing knowledge about recent state-of-the-art developments, best practices, and solutions in E&P technology. Each reviewer also picks additional papers for a recommended reading list, for those interested in more high-quality information on a topic, and prepares an article on the state of the technology in that particular discipline. So far this year, the committee has reviewed 3,795 papers and will have reviewed more than 4,000 by the end of the calendar year. The process is distinct, but sometimes confused, with peer review. SPE’s online technical journals publish peer-reviewed papers, which is a more lengthy process involving industry experts carefully evaluating a paper and working with the author to clarify or validate certain assumptions or statements.

Summary Stimulated reservoir volume (SRV) is a prime factor controlling well performance in unconventional shale plays. In general, SRV describes the extent of connected conductive fracture networks within the formation. Being a pre-existing weak interface, natural fractures (NFs) are the preferred failure paths. Therefore, the interaction of hydraulic fractures (HFs) and NFs is fundamental to fracture growth in a formation. Field observations of induced fracture systems have suggested complex failure zones occurring in the vicinity of HFs, which makes characterizing the SRV a significant challenge. Thus, this work uses a broad range of subsurface conditions to investigate the near-tip processes and to rank their influences on HF-NF interaction. In this study, a 2D analytical workflow is presented that delineates the potential slip zone (PSZ) induced by a HF. The explicit description of failure modes in the near-tip region explains possible mechanisms of fracture complexity observed in the field. The parametric analysis shows varying influences of HF-NF relative angle, stress state, net pressure, frictional coefficient, and HF length to the NF slip. This work analytically proves that an NF at a 30 ± 5° relative angle to an HF has the highest potential to be reactivated, which dominantly depends on the frictional coefficient of the interface. The spatial extension of the PSZ normal to the HF converges as the fracture propagates away and exhibits asymmetry depending on the relative angle. Then a machine-learning (ML) model [random forest (RF) regression] is built to replicate the physics-based model and statistically investigate parametric influences on NF slips. The ML model finds statistical significance of the predicting features in the order of relative angle between HF and NF, fracture gradient, frictional coefficient of the NF, overpressure index, stress differential, formation depth, and net pressure. The ML result is compared with sensitivity analysis and provides a new perspective on HF-NF interaction using statistical measures. The importance of formation depth on HF-NF interaction is stressed in both the physics-based and data-driven models, thus providing insight for field development of stacked resource plays. The proposed concept of PSZ can be used to measure and compare the intensity of HF-NF interactions at various geological settings.

Conventional well-log-based rock classification often overlooks rock-fabric features (spatial distribution of solid and fluid-rock components), which makes it not comparable against geologic facies, especially in formations with complex rock fabric. This challenge is usually addressed by the identification of geological facies from the core description and their integration with measured petrophysical properties. However, manual identification of geological facies using core data is a tedious and time-consuming process. In this paper, we propose an automatic workflow for joint interpretation of conventional well logs, computed tomography (CT) scan/core images, and routine core analysis (RCA) data for simultaneously optimizing rock classification and formation evaluation. First, we perform conventional well-log interpretation to obtain petrophysical properties of the evaluated depth intervals. Subsequently, we automatically extract rock-fabric-related features derived from core photos and core CT scan images. Then, we use a clustering algorithm to obtain rock classes from the extracted rock-fabric features. We optimize the number of rock classes by iteratively increasing the number of rock classes from an initially assumed number until a permeability-based cost function converges below a predefined threshold. The proposed workflow will provide (i) quantitative wellbore/core image-based rock-fabric- related features, (ii) automatic integration of rock-fabric-related features with conventional well logs and RCA data, and (iii) automatic and simultaneous assessment of rock classes and petrophysical properties, honoring rock fabric. Additionally, the outcomes of the proposed workflow can help to expedite the process of geological facies classification by providing an overview of different lithologies and an overall stacking pattern. We successfully applied the proposed workflow to a sedimentary sequence with vertically variable rock fabric and lithology. Dual-energy-acquired core CT scan images were available along with core photos, RCA data, and conventional well logs. Image-based integrated rock classes were in agreement with the lithologies encountered in the evaluated depth interval. Class-by-class permeability models improved permeability estimates by 89% (decrease in mean relative error) in comparison to formation-by-formation permeability estimates. Furthermore, the detected rock classes were consistently propagated to another well where core and CT scan images were not employed for rock classification. The detected rock classes were in agreement with lithofacies obtained from the core description. Permeability estimates were also in good agreement with available RCA data.