Executive Summary

Welcome to the November edition of the SPE Production & Operations journal. I always enjoy selecting papers that provide some form of theme for the issue, and this month I have managed to focus mostly on hydraulic fracturing. The last two fracturing papers discuss the chemistry of fracturing fluids, which provides a nice link into a small group of well-treatment papers, the first two of which are also chemistry papers. So, whilst there are two themes in this issue, I have managed to sneak in four chemistry papers. (Well, what would you expect from an executive editor who is a chemist?) Seriously, I hope that you like the mix of papers in this issue, which I think nicely reflects the breadth of our technical coverage. For me, this breadth is one of the joys of SPE Production & Operations and also one of the great benefits of attending multidisciplinary meetings such as the SPE Annual Technical Conference and Exhibition (ATCE). 

As I am sure you are aware, this year’s ATCE took place in Dubai (from 26 to 29 September), and, despite the current oil price environment, was attended by 7,500 delegates from 91 countries. More than 390 technical presentations were given, which I find remarkable. Many of these papers are currently undergoing peer review, so will appear in SPE journals in a few months’ time ( SPE Production & Operations has quite a number under review). However, all of the papers presented at the conference are available on OnePetro, so if you couldn’t attend ATCE this year, you can check out your favorite technical areas online.

Overview of Papers

The first paper in this issue— Diagnosis of Production Performance After Multistage Fracture Stimulation in Horizontal Wells by Downhole Temperature Measurements—discusses the use of downhole temperature measurements for fracture-treatment monitoring. Downhole temperature data measured by production logging tools or fiber-optic distributed-temperature sensors are used frequently to diagnose multistage fracture treatments in horizontal or highly deviated wells. This paper shows that temperature data can be used to identify fracture locations and estimate flow-rate distributions, allowing for a better understanding of the process of fracturing and the performance of fractured wells.

Optimum Fracture Conductivity for Naturally Fractured Shale and Tight Reservoirs discusses an approach to assess the amount of proppant injected by determining the optimum post-fracture conductivity through use of 3D finite-difference reservoir simulations in a naturally fractured reservoir, which has both hydraulic fractures and natural fractures. The post-fracture productivity of such low-permeability reservoirs is largely determined by the matrix/fracture contact area with appropriate fracture conductivity. Although it is often anticipated that the fractures are infinitely conductive, the general belief is that production increases with the proppant amount injected. This work shows that the critical conductivity increases with propped length and production time. Complex fracture networks have become more evident in shale reservoirs as a result of the interaction between pre-existing natural fractures and hydraulic fractures.  

Numerical Investigation of Complex Hydraulic Fracture Development in Naturally Fractured Reservoirs discusses simulated simultaneous multiple-fracture propagation within a single fracturing stage by use of a complex hydraulic-fracture development model. The model was developed to simulate complex fracture propagation by coupling rock mechanics and fluid mechanics. A simplified 3D displacement-discontinuity method was implemented to more accurately calculate fracture displacements and fracture-induced dynamic-stress changes.

In a change of emphasis, Proppant-Conveyer Automation System With Cascade Control in Hydraulic Fracturing discusses a proppant-conveyor automation system that automatically delivers proppant for hydraulic fracturing, which improves working conditions and reduces environmental pollution significantly.

Changing our focus, Supramolecular Fluid of Associative Polymer and Viscoelastic Surfactant for Hydraulic Fracturing discusses a new fracturing fluid that is based on a supramolecular complex between associative polymer and viscoelastic surfactant (VES). The concentration of surfactant in the new fluid is 10 times less than that of a conventional VES fracturing fluid, and the combination of VES and associative polymer synergistically enhances the viscosity to several times more than that of the individual components alone. The fluid system was optimized by experimental design. 

Hydraulic fracturing can be used for stimulating low-permeability heavy-oil reservoirs. However, it is challenging to achieve a high degree of fracturing-fluid flowback, as well as a low degree of formation damage in these reservoirs. Application of Novel Hyperbranched-Polymer Fracturing-Fluid System in Low-Permeability Heavy-Oil Reservoir investigates the application of a novel hyperbranched-polymer fracturing fluid in low-permeability heavy-oil reservoirs. Laboratory tests are conducted to evaluate the thermal stability, shearing resistance, reversible-crosslinking performance, salinity tolerance, static-filtration performance, gel-breaking performance, and sand-carrying performance of the polymer. 

Finally, although we keep with our chemistry theme, we have three papers that describe well treatments. Laboratory Testing of Environmentally Friendly Sodium Silicate Systems for Water Management Through Conformance Control discusses the laboratory screening and evaluation of mixtures of existing commercial, environmentally friendly, sodium silicate chemicals that can be used for water management in naturally fractured carbonate reservoirs. This work investigates different combinations of sodium silicate with two types of polymer—a biopolymer (xanthan) and a low molecular weight synthetic polymer.  

Acid stimulation, for both oil and gas wells, is a versatile means of enhancing production. Although acids enhance carbonate reservoir permeability to hydrocarbons, the reaction rates of the acid (e.g., hydrochloric acid [HCl]) with the rock often are too rapid at high temperatures, leading to a reduction in acid penetration. Several methods exist to improve the effectiveness of acidizing in high-temperature reservoirs (e.g., greater than 120°C), including the use of conventional emulsified-acid systems, mixtures of HCl and organic acids, and gelled acids. All of these systems have drawbacks.  A novel deployment method that overcomes these problems is discussed in Core/Shell Systems for Delayed Delivery of Concentrated Mineral Acid. This paper describes a tunable core/shell delivery system that allows much deeper penetration of strong acid into the reservoir.

Our final paper in this issue is not directly a chemistry paper, but does uses a technique that is very familiar to chemists. NMR as a Characterization Tool for Wormholes discusses an improved nuclear magnetic resonance (NMR) technique to study the formation of acid-induced wormholes in laboratory-based core plug experiments. If acidizing is used on carbonate reservoirs, the acids tend to create conductive channels (wormholes) that connect the reservoir to the wellbore and bypass the damaged zones. This novel technique allows this process to be studied in detail to allow optimization of field treatments.

I hope that you enjoy these papers, and don’t forget that many more are available online via OnePetro ( https://www.onepetro.org), so please do have a browse and see what is new in your field. 

Ian Collins, BP Exploration