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Massive hydraulic fracturing has been successfully applied in tight gas reservoir development. Economic completion of tight gas sands with large hydraulic fracturing treatments requires cost effective and time saving operations. Traditional large fracturing jobs are usually pumped down 5.5" or 4.5" casing to meet the requirement of high pumping rate (30~55bpm). Post-frac snubbing operations are often needed to run tubing and clean out wellbores. Snubbing operations can be costly in terms of investment and time. Annular fracs have been applied in the industry as an alternative completion strategy. However, previously documented annular jobs have been small size, ranging from 40k to 200k lbs of proppant pumped at relatively low injection rates of 15–25 BPM. This paper describes the practices of massive annular fracturing treatments down the 5–1/2" by 2–3/8" annulus used at the Bajiaochang Gas Field, Sichuan Basin, China, as a substitute to fracturing down casing and subsequent snubbing operations. Three treatments have been performed since October 2005. The first job had to be terminated with 70% of the designed proppant (394k lbs) pumped because of the failure of the blast joint. Lessons learned were outlined and modifications were made to the blast joint and wellhead. Subsequent treatments were performed without mechanical failures with 350k and 282k lbs of proppant pumped at 30 to 35 bpm injection rates. The completion cycle time was reduced about 20% with substantial savings of up to $260k in well completion costs. Improved monitoring of bottom hole pressure from static tubing for 3D fracture modeling and effective treatment evaluation were also a benefit. This data has aided fracture design in highly complex fracture stimulation applications. Additional advantages also include: easily circulating out proppant if screen outs occur and more efficient flow back for lower rate wells. Introduction: A tight gas sand exploration and development program has been on going for several years in Chuanzhong Block, Sichuan Basin, China. The reservoir is a fluvial deposit which is located in a slight thrust-fault environment with a possible small strike-slip component. It is over-pressured with micro-Darcy permeability sand (See Figure 1–2). Fifteen wells have been drilled by the operator. All wells are completed in the gas-bearing XX-4 formation at depths of approximately 3150m MD (about 3000m TVD, "S" shape wells are drilled from multi-well pads) by utilizing massive hydraulic fracturing treatments that are the largest and the most complicated in China. The general completion practice at Bajiaochang had been traditional cross-linked gel fracs pumped down 5–1/2" casing at rates from 40 - 50 BPM. Other frac designs including slick water treatment and hybrid fracs have also been used. Due to the potential for waterblocks, post-frac snubbing operations were performed to run production tubing and wash out sand while maintaining an underbalanced wellbore condition. Generally, the completion cycle time was around 41days before handing well over to production. The majority of the fracturing treatments were designed by using the 3D Mfrac model. Real time data has been monitored by linking-up a laptop to the treatment van computer for fracture evaluation and re-design on-site. Lack of bottom hole pressure measurement makes it very difficult to estimate the complex fracture behavior in this high stress environment. Estimation from surface treating pressure, which includes variable friction, may lead to erroneous interpretations.
Massive hydraulic fracturing has been successfully applied in tight gas reservoir development. Economic completion of tight gas sands with large hydraulic fracturing treatments requires cost effective and time saving operations. Traditional large fracturing jobs are usually pumped down 5.5" or 4.5" casing to meet the requirement of high pumping rate (30~55bpm). Post-frac snubbing operations are often needed to run tubing and clean out wellbores. Snubbing operations can be costly in terms of investment and time. Annular fracs have been applied in the industry as an alternative completion strategy. However, previously documented annular jobs have been small size, ranging from 40k to 200k lbs of proppant pumped at relatively low injection rates of 15–25 BPM. This paper describes the practices of massive annular fracturing treatments down the 5–1/2" by 2–3/8" annulus used at the Bajiaochang Gas Field, Sichuan Basin, China, as a substitute to fracturing down casing and subsequent snubbing operations. Three treatments have been performed since October 2005. The first job had to be terminated with 70% of the designed proppant (394k lbs) pumped because of the failure of the blast joint. Lessons learned were outlined and modifications were made to the blast joint and wellhead. Subsequent treatments were performed without mechanical failures with 350k and 282k lbs of proppant pumped at 30 to 35 bpm injection rates. The completion cycle time was reduced about 20% with substantial savings of up to $260k in well completion costs. Improved monitoring of bottom hole pressure from static tubing for 3D fracture modeling and effective treatment evaluation were also a benefit. This data has aided fracture design in highly complex fracture stimulation applications. Additional advantages also include: easily circulating out proppant if screen outs occur and more efficient flow back for lower rate wells. Introduction: A tight gas sand exploration and development program has been on going for several years in Chuanzhong Block, Sichuan Basin, China. The reservoir is a fluvial deposit which is located in a slight thrust-fault environment with a possible small strike-slip component. It is over-pressured with micro-Darcy permeability sand (See Figure 1–2). Fifteen wells have been drilled by the operator. All wells are completed in the gas-bearing XX-4 formation at depths of approximately 3150m MD (about 3000m TVD, "S" shape wells are drilled from multi-well pads) by utilizing massive hydraulic fracturing treatments that are the largest and the most complicated in China. The general completion practice at Bajiaochang had been traditional cross-linked gel fracs pumped down 5–1/2" casing at rates from 40 - 50 BPM. Other frac designs including slick water treatment and hybrid fracs have also been used. Due to the potential for waterblocks, post-frac snubbing operations were performed to run production tubing and wash out sand while maintaining an underbalanced wellbore condition. Generally, the completion cycle time was around 41days before handing well over to production. The majority of the fracturing treatments were designed by using the 3D Mfrac model. Real time data has been monitored by linking-up a laptop to the treatment van computer for fracture evaluation and re-design on-site. Lack of bottom hole pressure measurement makes it very difficult to estimate the complex fracture behavior in this high stress environment. Estimation from surface treating pressure, which includes variable friction, may lead to erroneous interpretations.
This paper illustrates a comprehensive and economical approach to the application of reservoir data to optimize stimulation designs. The paper documents the selective application of in situ stress tests and dipole sonic logs to provide accurate stress profiles that can be used in concert with standard log and minifracture data to improve stimulation designs.:.Measured stress data on 3 wells were used to calibrate open-hole logs to provide an estimate of stress profiles throughout a 300 square mile area of the Moxa Arch. Dipole sonic log-derived stress profiles were correlated to measured stress data. Calibrated stress profiles from dipole sonic logs and the measured stress data were then, used, to develop a correlation between gamma-ray logs and in situ stress. The log-based stress data was improved with the addition of over 50 mini-fracture tests. The combination of selected stress measurements, dipole sonic logs, and mini-fracture treatments resulted in optimized stimulation designs and cost savings of over $100,000 per well.
This paper demonstrates a methodical approach in the implementation of current hydraulic fracturing technologies. Specific examples illustrating the evolution of a consistent reservoir/hydraulic fracturing interpretation are presented in a case history of three GRI-Industry Technology Transfer wells. Detailed modeling of these project wells provided an overall reservoir and hydraulic fracture description that was consistent with respect to all observations. Based on identification of the fracturing mechanisms occurring, the second and third project wells show the capabilities of real- time diagnostics in the implementation of hydraulic fracture treatments. By optimizing the pad volume and fluid integrity to avoid premature screenouts, significant cost savings and improved proppant placement were achieved. The production and pressure build-up response in the first project well verifies the overall interpretation of the reservoir/hydraulic fracture model and provides the basis for eliminating the use of moderate strength/higher cost proppant over sand in low permeability/higher closure stress environments. Introduction The successful implementation of an applied hydraulic fracturing project requires a balanced mix of data acquisition combined with applied field implementation projects. What results from a project of this type is a reservoir and hydraulic fracturing interpretation that matches what actually occurs both during the fracture treatment and also during the actual production response. Once this type of interpretation is achieved, significant optimization can occur to provide the minimum cost for the best economic results. Ideally, the data acquisition is mixed with the field implementation efforts in order to high grade the interpretation and quality of the data and minimize cost resulting from impractical applications, unnecessary data or an overkill of data acquisition efforts. Each step of a project should be pursued by methodically weighing the cost/benefit of each data acquisition and field implementation effort. The basic framework for an applied hydraulic fracturing project consists of the following phases: P. 85
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