Multistage Stimulation: Fracturing Optimization at Samotlorskoe Field

Abstract

Accelerated multi-stage hydraulic fracturing at the Samotlor Field significantly contributes to the reduction of time and financial costs for well construction and well interventions. High friction pressure loss is one of the main causes of complications, extra process operations, and, as a result, extra time and financial costs for multi-stage hydraulic fracturing with selective packers and burst port collars. A comprehensive analysis of MS frac data and testing of new approaches to mini-frac confirmed a potential significant reduction in MS frac costs at the Samotlor Field. The work consisted of three stages. The first stage included the following: Compared the data from wellhead and downhole gaugesAnalyzed in-situ temperature profileAnalyzed the results of Step Down Tests (SDT)Identified patterns of pressure changes in the bottomhole and near-wellbore zonesAnalyzed the causes of high working pressures at collar activation stages. The second stage covered a mini-frac pilot against a modified approach: Cancelled Step Down TestsIncreased planned fluid ratesCancelled a mini-frac with proppantDetermined methods for optimizing the main hydraulic fracturing. The third stage confirmed the efficiency of new approaches to multi-stage hydraulic fracturing with a selective packer and burst port collars at the Samotlor field. The paper analyzes the data on wells with the following types of completions: 34 wells with cemented liners14 wells with non-cemented liners with swellable packers. 330 hydraulic fracturing stages were analyzed. The sensitivities of friction changes in the bottomhole zone and the frac collar zone to various factors were evaluated: Number and types of injection jobsFluid flow rateEffect of hydraulic fracturing fluid and abrasive effects of proppant. The design features of internal-flush sleeves with burst port collars were studied and factors affecting fluid flow restrictions in the near-wellbore formation zone were determined. Based on the analysis, recommendations were made to optimize injection jobs during a pilot and the main hydraulic fracturing. Pilot jobs were carried out in 40 wells, which included 150 stages without traditionally performed test injections (a step-down test with a decrease in flow rate and a calibration test on crosslinked fluid with proppant). The tested methods allowed to accelerate the hydraulic fracturing process, reduce the volume of injected fluid, speed up the decision-making process related to field jobs, which led to accelerated operations and reduced cost of multi-stage hydraulic fracturing at the Samotlor Field. The novelty of the work lies in the development and justification of an individual approach to a set of test studies and the types of changes in hydraulic fracturing programs depending on subsurface and engineering factors, working pressure profile, and estimated friction losses. As mentioned earlier, the proposed approach will significantly reduce the time and financial costs of multi-stage hydraulic fracturing at the Samotlor Field. The approaches can be adjusted and rolled-out to other fields in case of applying burst port collars and selective packers.