Fracturing Technologies with Profile Control and Water Shutoff for Medium and High Water-Cut Wells in Ultra-Low Permeability Reservoirs of Changqing Oilfield

DA Yinpeng1,2 LI Jianhui1,2 WANG Fei2,1 HUANG Ting1,2 XUE Xiaojia1,2 YU Jinzhu1,2

(1.Oil & Gas Technology Research Institute, PetroChina Changqing Oilfield Company, Xi’an, Shaanxi 710018)
(2.National Engineering Laboratory of Low Permeability Oil and Gas Field Exploration and Development, Xi’an, Shaanxi 710018)
【Novelty】The main ultra-low permeability reservoirs in the Changqing Oilfield are the ones in the Triassic Yanchang Formation, and they have entered the medium and high water-cut development stage. Conventional refracturing is prone to increasing water cut after oil well measures and consequently affects the improvement of the ultimate recovery of those reservoirs. Therefore, fracturing technology plugging old fractures and fracturing new ones should be investigated. According to the development characteristics of the Chang 6 Reservoir in Block S127 of the Ansai Oilfield, this paper studied the production increasing mechanism of fracturing with profile control and water shutoff of medium and high water-cut wells in ultra-low permeability reservoirs. Then, it analyzed the influences of different parameters of fracturing with profile control and water shutoff on the repeated stimulation effect of the wells and proposed the refracturing idea of “profile control and water shutoff in the pad adding stage to control water cut and dynamic multi-stage temporary plugging fracturing to improve single-well production.” A matching PEG-1 gel was also developed to serve as a profile control/water shutoff agent in the pad adding stage, and the process of fracturing with profile control and water shutoff was optimized. The remaining oil in the lateral high-stress zone of old fractures was thereby effectively produced. Field tests were conducted in five wells in the Changqing Oilfield, and favorable oil production increase and water control effects were achieved. This research provides a new technical approach for refracturing medium and high water-cut wells in this oilfield.

【Abstract】Due to the influence of the high-permeability zone, the water cut will increase and reservoir stimulation results are poor when conventional refracturing is implemented in the ultra-low permeability reservoirs of Changqing Oilfield at the medium and high water-cut development stage. Focusing on the long-term injection-production development practices of typical reservoirs and infill well production data, this paper uses 3D geological modeling to analyze the stimulation mechanism of fracturing with profile control and water shutoff in medium and high water-cut oil wells. The influence of fracturing parameters on the effect of repeated stimulation was studied, and a refracturing concept hinging on “profile control and water shutoff in the pad adding stage to control water cut and dynamic multistage temporary plugging fracturing to improve single-well production” was advanced. PEG-1 gel was developed through laboratory experiments and when the mass fraction of its main agent achieved 5%–10%, gel strength would be maintained at a high level. With an optimal injection flow rate of 1.5 m3/min and an injection volume of 300–600 m3, the high-permeability zones at the fracture depth of 40–80 m could be effectively plugged. In this way, the dynamic multistage temporary plugging fracturing technology was optimized. As a result, the net pressure in the fractures was increased to above 5.0 MPa, fractures extended from the low-stress zone to the high-stress zone, and the production of the oil remaining laterally was thereby produced. Field test results showed that average oil production improvement per well was 1.07 t/d and water cut was reduced by 9 percentage points after the measure was implemented, which indicated that the goal of increasing oil production while controlling water was accomplished by refracturing the medium and high water-cut wells. The proposed fracturing technology with profile control and water shutoff provides a new technical concept for the repeated stimulation of medium and high water-cut wells in ultra-low permeability reservoirs of Changqing Oilfield.

【Keywords】 ultra-low permeability reservoir; medium and high water-cut well; fracturing with profile control and water shutoff; oil production increase and water control; Changqing Oilfield;

【DOI】

【Funds】 Exploration and production project of PetroChina Company Limited (2102-2-2)

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(Translated by YAO J)

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This Article

ISSN:1001-0890

CN:11-1763/TE

Vol , No. 03, Pages 74-79

May 2022

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Abstract

  • 1 Stimulation mechanism of fracturing with profile control and water shutoff
  • 2 Key technology for fracturing with profile control and water shutoff
  • 3 Field test
  • 4 Conclusions and recommendations
  • References