Diagnostic Pumping Tests to Optimize Fracturing Designs in the Harsh Environment of Western Siberia
Abstract: TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractHydraulic proppant fracturing continues to rapidly evolve in western Siberia/Russia and is seen as the most important and effective means to improve oil production from existing, as well as, newly drilled wells.Fracture treatments in Russia were traditionally small, conservative treatments with small-sized proppants and inefficient fracturing fluids. They were designed with a onesize-fits-all approach to bypass near-wellbore damage rather than provide sustain… Show more
Search citation statements
Paper Sections
Citation Types
Year Published
Publication Types
Relationship
Authors
Journals
Cited by 4 publications
References 13 publications
Hydraulic fracturing has probably become the most attractive solution to enhance production in the oil fields of Russia and western Siberia in particular. Besides optimizing the fracturing design with the ultimate goal of increased production, it is equally important that optimized fracturing treatments be pumped successfully in the field. Only a high success rate with a limited number of screenouts can help guarantee that production optimization will be achieved. It is also important to reduce downtime, for operators to have earlier production, and for service providers to optimize equipment utilization. In western Siberia, harsh conditions exist all year round. The winters are long with temperatures way below freezing for several months in a row. The summers are short, but can be quite warm. Logistics are difficult due to these weather conditions and because roads are rarely in good shape and worksites may be located very far away from equipment bases. To achieve success under these conditions, a lot of emphasis must be placed on quality control (QC) and quality assurance (QA). QC/QA must address many issues on the equipment side due to the harsh environment, but just as important is materials, in particular materials required for preparing the frac fluid and to a smaller extent the proppant used to hold the fractures open. The frac fluid itself creates the biggest QC/QA challenge. Of special importance is the mixing water because the sources for mixing water vary and the quality of the water changes seasonally. Stringent QC/QA procedures must be in place, including fluid testing under actual reservoir conditions to check the performance of the frac fluid downhole. This paper describes processes that have been developed and implemented in western Siberia. It includes equipment checks and maintenance as well as QC/QA procedures for frac fluids and their components and proppants. Specific issues related to the special location will be discussed and solutions presented regarding how a successful frac treatment can be provided every time. Introduction Propped hydraulic-fracturing design has evolved significantly over the past decade, in particular for Siberia and for Russia in general. Although today small treatments (5-15 metric tons [MT]) are still being performed, mainly to bypass near-wellbore damage, many companies have adopted a proper frac design and overall production optimization approach. This means that treatments are designed to optimize production based on the specific well and reservoir parameters for each field. Treatments sizes of 200-300 MT are common, and the average proppant volume pumped per treatment is around 80-100 MT in areas where operating companies have taken on this engineered approach. Currently, treatment design is one issue, while job execution is another. Without proper execution, the production increase predicted by simulation models based on the designed fracture geometry will not be obtained. It is therefore critical that all parts of a fracturing treatment execution be controlled in a way that the designed frac geometry (and with it, conductivity and production) will be delivered. This paper discusses propped hydraulic-fracturing treatments and it is assumed that wells have been prepared as required with proper casing, cementation of the casing, perforations, and wellhead installations to allow pumping the designed treatment. It is also assumed that all post-frac treatment cleanout and workover procedures are performed so that no damage to the already created fractures will occur. The particular subjects of this paper are equipment, fluids, and proppant. Each plays an important part in eliminating "execution" from the equation for delivering the best fracturing treatment. Only then are engineering teams able to focus their attention on other design and reservoir related issues. Although other issues are important to overall success and worthy of full attention, they will not be discussed in this paper, including perforating,1 cleanout, workover, pump selection, or other peripheral subjects. The main task of both operating and service companies is to deliver the optimum well performance. Several fracturing treatments result in early termination of the treatment due to what is generally described as screenout. Screenout is a process that needs to be looked at carefully.
Hydraulic fracturing has probably become the most attractive solution to enhance production in the oil fields of Russia and western Siberia in particular. Besides optimizing the fracturing design with the ultimate goal of increased production, it is equally important that optimized fracturing treatments be pumped successfully in the field. Only a high success rate with a limited number of screenouts can help guarantee that production optimization will be achieved. It is also important to reduce downtime, for operators to have earlier production, and for service providers to optimize equipment utilization. In western Siberia, harsh conditions exist all year round. The winters are long with temperatures way below freezing for several months in a row. The summers are short, but can be quite warm. Logistics are difficult due to these weather conditions and because roads are rarely in good shape and worksites may be located very far away from equipment bases. To achieve success under these conditions, a lot of emphasis must be placed on quality control (QC) and quality assurance (QA). QC/QA must address many issues on the equipment side due to the harsh environment, but just as important is materials, in particular materials required for preparing the frac fluid and to a smaller extent the proppant used to hold the fractures open. The frac fluid itself creates the biggest QC/QA challenge. Of special importance is the mixing water because the sources for mixing water vary and the quality of the water changes seasonally. Stringent QC/QA procedures must be in place, including fluid testing under actual reservoir conditions to check the performance of the frac fluid downhole. This paper describes processes that have been developed and implemented in western Siberia. It includes equipment checks and maintenance as well as QC/QA procedures for frac fluids and their components and proppants. Specific issues related to the special location will be discussed and solutions presented regarding how a successful frac treatment can be provided every time. Introduction Propped hydraulic-fracturing design has evolved significantly over the past decade, in particular for Siberia and for Russia in general. Although today small treatments (5-15 metric tons [MT]) are still being performed, mainly to bypass near-wellbore damage, many companies have adopted a proper frac design and overall production optimization approach. This means that treatments are designed to optimize production based on the specific well and reservoir parameters for each field. Treatments sizes of 200-300 MT are common, and the average proppant volume pumped per treatment is around 80-100 MT in areas where operating companies have taken on this engineered approach. Currently, treatment design is one issue, while job execution is another. Without proper execution, the production increase predicted by simulation models based on the designed fracture geometry will not be obtained. It is therefore critical that all parts of a fracturing treatment execution be controlled in a way that the designed frac geometry (and with it, conductivity and production) will be delivered. This paper discusses propped hydraulic-fracturing treatments and it is assumed that wells have been prepared as required with proper casing, cementation of the casing, perforations, and wellhead installations to allow pumping the designed treatment. It is also assumed that all post-frac treatment cleanout and workover procedures are performed so that no damage to the already created fractures will occur. The particular subjects of this paper are equipment, fluids, and proppant. Each plays an important part in eliminating "execution" from the equation for delivering the best fracturing treatment. Only then are engineering teams able to focus their attention on other design and reservoir related issues. Although other issues are important to overall success and worthy of full attention, they will not be discussed in this paper, including perforating,1 cleanout, workover, pump selection, or other peripheral subjects. The main task of both operating and service companies is to deliver the optimum well performance. Several fracturing treatments result in early termination of the treatment due to what is generally described as screenout. Screenout is a process that needs to be looked at carefully.
Before the mid-1990s, the main goal of hydraulic-fracturing operations in Russia was preventing near wellbore damage. Typical fracturing treatments used a crosslinked polymer-based gel as carrier fluid to place 5 to 20 MT of proppant into the formation. Because of the results, a new phase started, whereby "real" production enhancement treatments achieving skins of well beyond -4 were pumped with proppant volumes from 50 to over 100 MT. Because of Russian oil production practices at the time, it became apparent that the hydraulic fracturing technology combined with drilling horizontal wells increased production and was therefore beneficial to the Russian economy. When the optimization process started, quality control in the field became mandatory in addition to an enhanced focus on health, safety and environment. Service companies focused on cleaner fluids with less polymer loadings and better breaker systems. Prejob, on-the-job, and postjob quality control procedures were developed specifically for the Russian environment and reached a standard unlike anywhere else in the world. The number of unwanted screenouts was reduced significantly by following proper perforating practices and optimizing the treatments designs in real time. The new goal was a skin of -5, and the design process was optimized to achieve this number by designing each job to achieve optimum production for the given reservoir parameters, especially permeability. Treatments of 300–400 MT are not uncommon these days for low permeability reservoirs with a large reservoir height sometimes covering several zones. This lead to the optimization process that is currently practiced. Because many sandstone reservoirs, particularly in Siberia, are laminated, the vertical permeability is often an order of magnitude or more lower than compared to the horizontal permeability. Several times, horizontal wells did not yield the expected results. Hydraulic fracturing treatments placed in the horizontal wellbore can be the solution for further production optimization. This paper describes how this can be established through several techniques. Hydraulic fracturing includes propped hydraulic fracturing in both oil and gas reservoirs, as well as carbonate fracture acidizing. This paper discusses propped hydraulic fracturing in oil reservoirs. Covering propped hydraulic fracturing in gas reservoirs, although still at the beginning stages, could reveal enough material for a paper on its own. However, carbonate fracture acidizing is not frequently used. Introduction In 2009, the oil and gas industry will celebrate 60 years of hydraulic fracturing. In March, 1949, a team of Halliburton Oil Well Cementing Company and Stanolind Oil Company personnel gathered at a wellsite near Duncan, Oklahoma, U.S.A., to make oilfield history by performing the first commercial hydraulic-fracturing treatment (Fig. 1). Tens of thousands of wells have been treated using this technology and several improvements have been made since in the Western world. Exploration for oil was active in the former Soviet Union in the 1840s in the vicinity of Baku (the first modern oil well was drilled in 1846 by Russian engineer F.N. Semyenov) in the Caspian and was revived significantly after World War II. Soviet explorers were able to apply scientific methods free of commercial constraints. Boreholes were drilled for geological information and Russian explorers pioneered the geochemical breakthrough that identified the source rocks and generating belts.
Screenouts of Propped Hydraulic Fracture (PHF) treatments have numerous failure causes, namely, Near-Wellbore Friction, Deviatoric stress, Non-compliant geologic formations, Multiple fractures, Segmented en-echelon fractures, Backstress due to pressure depletion, and, Fracture-tip dilatancy. This paper focuses on the newly-introduced parameter of the Median Ratio (MR) of the Rate Step-down Test (RST) and Near-wellbore (NWB) friction, both of which must be used concurrently as Proppant Admittance (PA) criteria, because screenout causes are not failure diagnosis methods, therefore, not useful in predicting, and/or avoiding screenouts. Each of the PA criteria, while necessary for diagnosis, is not sufficient for accurate prediction of screenout potential, because, when each PA criterion is considered separately it is accurate in 40–45% of the cases, whereas, when both of the PA criteria are used concurrently prediction accuracy increases to over 95%. Therefore, both PA criteria are necessary for accurate Fracture Entry Friction (FEF) analysis, and, prediction of screenout potential. The MR can be determined easily, rapidly, and accurately with the proposed four-equal-step RST procedure. The MR is an empirical function defined as: MR=DP4 / DP1. Concurrent occurrence of: 1) a MR value greater than 0.5, and, 2) a NWB friction value greater that 30 bar (435 psi) is considered: a) an anomaly, b) it is indicative of higher than normal NWB friction, and, c) it is the threshold for PA problems. Both the MR and NWB friction are calculated accurately with enhanced FEF analysis of the RST. The RST has a very short duration, during which, all parameters remain constant: wellbore configuration, perforation configuration, fluid parameters, and fracture dimensions (length, width and height). In addition, pressure loss due to friction is a function of flowrate; hence, progressively smaller pressure reduction steps should be noted as the rate is reduced during the RST. Because all parameters are constant, any deviation from the expected pattern of progressively decreasing pressure loss steps is a strong indication of hindrance to fluid flow, and can only be caused by a restrictive NWB area, and the associated NWB friction. Therefore, the MR and NWB friction are powerful diagnostic criteria of PA, which are useful for the successful design and placement of PHF treatments. The methodology of concurrent usage of the MR and NWB friction, and of the specific four-step RST procedure, has been tested extensively on numerous PHF treatments, in both geologically and geographically diverse conditions. We demonstrate that they provide a high-level of confidence required for pre-mainfrac redesign and modifications to the completion, the treatment procedure, and the treatment schedule, and also, for on-the-fly, real-time decision and control. Utilized wisely, the methodology increases the probability of achieving safe and effective placement of PHF treatments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
Contact Info
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Product
Resources
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.
