Executive Summary

Welcome to the May issue of SPE Production & Operations. There was a rich selection of papers to choose from for this issue, so I decided to focus on three areas to give you a diverse choice of papers. This issue focuses on the application of chemical science to production problems, understanding hydraulic-fracture performance in complex reservoirs, and wells technology. As ever, I enjoyed selecting the papers for this issue because it allowed me to try and understand topics in production operations that I’m not too familiar with. I find that trying to understand technical areas that are outside of my current technical domain is really useful in understanding how my expertise can impact different areas of upstream technology. I encourage you to use the resources that are offered by SPE to not only deepen your own domain expertise, but also to learn something new in a seemingly unrelated area—you may find that they are not so unrelated after all! SPE provides an excellent range of resources to help with this and I encourage you to browse the website.

Chemistry

The first paper in this issue (Mitigation of the Effects of Condensate Banking: A Critical Review) discusses the fiendishly difficult-to-manage problem of condensate banking scaling. Several techniques have been used to mitigate condensate banking. These methods include gas cycling, drilling horizontal wells, hydraulic fracturing, injection of super critical CO2, use of solvents, and the use of wettability alteration chemicals. Each method has its own advantages and disadvantages, which are discussed in this paper together with a description of field trials performed and case studies that have been presented.

Reactive-Dissolution Modeling and Experimental Comparison of Wormhole Formation in Carbonates with Gelled and Emulsified Acids discusses 3D numerical simulation of carbonate acidization with hydrochloric acid, gelled acid, and emulsified acid by use of two-scale continuum models. The effect of transport and rheological properties of these non-Newtonian acids on the acidization and dissolution process is analyzed and compared with laboratory data.

Continuing with our chemistry theme is Laboratory Studies on Fluid-Recovery Enhancement and Mitigation of Phase Trapping by Use of Microemulsion in Gas Sandstone Formations, which describes a specific solution to the problem of water trapping following hydraulic fracturing. More than 60% of the injected fluid can remain in the critical near-wellbore region following a slickwater hydraulic-fracturing treatment in gas reservoirs. This has a significant negative impact on the relative permeability to gas and well productivity. This paper examines the effectiveness of microemulsions in the improvement of fluid recovery in sandstone cores with a permeability of greater than 10 md, focusing in particular on a novel microemulsion formulation.

Hydraulic Fracturing

We start our discussion of hydraulic fracturing with a paper that is linked to our previous topic. Evaluating Fracture-Fluid Flowback in Marcellus Using Data-Mining Technologies describes the use of post-hoc analysis to identify correlations between fracture-fluids flowback and attributes of the well completion and geological setting. This is then used to identify the factors that are most important in predicting flowback. Important factors identified to influence flowback efficiency are the number of hydraulic-fracture stages, lateral length, vertical depth, applied proppant mass, proppant size, applied fracture-fluid volume, treatment rate, and shut-in time.

We move on to a related paper (Water-Induced Damage to Propped-Fracture Conductivity in Shale Formations) that discusses how shale fracture conductivity can be reduced significantly by shale/water interactions. Factors that may influence shale fracture conductivity include shale mineralogy, proppant embedment, shale-fines migration, proppant-fines migration, brine concentration, longer-term stress application, and residual water in the fracture. The results of the study showed that clay content determines the fracture-conductivity damage caused by water. Fines generated from the shale fracture can migrate inside the fracture and are responsible for 12 to 15% of the conductivity reduction. A theoretical model of propped fracture conductivity was developed to include the effects of water damage on fracture conductivity.

Wells Technology

Our final topic covers well technology. Development and Field Trial of the Well-Lateral-Intervention Tool describes the development of an intelligent, real-time controllable tool, the well-lateral-intervention tool, that can identify a lateral junction and steer an intervention/surveillance string into it to overcome the current problems associated with accessing laterals reliably. The tool is designed to be deployed by either coiled tubing or by e-line. The paper describes the development stages of the tool and the field-trial results.

Estimation of Production Rates by Use of Transient Well-Flow Modeling and the Auxiliary Particle Filter: Full-Scale Applications demonstrates the use of a detailed transient multiphase well-flow model and an auxiliary sequential-importance resampling filter, for better representation of flow rates in wellbores (inflow and outflow). Two case studies are presented. The first is an application to an inclined gas producer with two inflow reservoir zones. Observations consist of pressure and temperature at two locations in the well. The next case study is an application to an inclined water injector with nine outflow zones. The results of these studies clearly demonstrate the feasibility of the automatic identification of reservoir flow-rate distribution from wellbore measurements.

Design and Analysis of Leak-Testing Methodology for Gas Lift Valves details the development of a forward model that helps design methodology for gas lift valve testing (such testing normally entails the monitoring of the transient pressure response). The model recommends drawing down the annular gas to develop a positive pressure differential to allow fluid flow from the tubing into the annulus through the suspected gas lift valve. This drawdown test is followed by a pressure buildup test. The model also allows the estimation of the time needed for each segment of the transient test sequence, thus helping to schedule such tests appropriately.

Well, that’s it for this issue. I just wish that we could feature more papers per issue because there are so many excellent ones accepted by the journal. However, they are all available online, so please do have a browse and see what is new in your field. Whilst you are online, take a look at the SPE events page (http://www.spe.org/events/calendar/) to see if there are any meetings or other events that might be of interest. Likewise, take a look at the webinars that are available (https://webevents.spe.org/).  Whilst browsing the recorded webinars, I came across one on wellbore strengthening that I will be definitely watching!

Ian Collins, BP Exploration