Novel Technology to Improve Recovery of Remaining Oil in Tight Glutenite Reservoir of Junggar Basin: Employing Chemical Diverting Agents in Refracturing Operation

Abstract

The production wells in tight glutenite reservoirs have great potential for refracturing, because most of fracturing fluid and proppant flow into the first-class layer with lower initiation pressure during initial stimulation with multi-layer simultaneous fracturing treatment. However, layer segmentation during refracturing can be a challenge, especially in vertical wells. Using only mechanical segmentation tools is of high risk and sometimes ineffective. This paper presents a new refracturing technology for vertical wells employing diverting agents. The segmentation tools are rarely needed in the new refracturing technology. The implementation procedures are as follows: First, reservoir characteristics, remaining oil distribution and water content are evaluated to identify the target layers of refracturing. Second, through the classification of predicted initiation pressure, number of temporary plugging and diverting fracturing are determined. The dosage of chemical diverting agents is designed. Finally, refracturing treatment are performed with an injection procedure of "fracturing fluid and proppants (dredging existing fractures) + granular plugging agents (blocking existing fracture entrances) + fracturing fluid and proppants (creating new fractures) + powdery plugging agents (blocking new fracture tips) + fracturing fluid and proppants (creating complex fracture networks)". The refracturing treatment was performed in Well B1401 located at Junggar Basin in China using the method presented in this paper. The fracturing construction curve of Well B1401 shows that obvious pressure increase was observed when the diverting agents was added, and the initiation pressure or propagation pressure of subsequent fracture was monitored higher than that of previous fracture. It is suggested that proper agents or combinations can effectively plug the opened fractures and generate high enough pressure in the fractures to initiate branch fractures. The production log data indicate that five new layers begin to produce oil after refracturing operation, and the daily oil production of Well B1401 remarkably increased from 1.5 t/d to 9.8 t/d in the field test, which verifies the validity of the tool-free refracturing of vertical wells employing diverting agents. This study provides a new refracturing technology for vertical wells in tight glutenite oil reservoir employing diverting agents is presented. The segmentation tools are rarely needed in the new refracturing technology. It has been applied to hundreds of low-yielding oil wells in tight glutenite reservoirs of Junggar Basin, China. The average annual oil production per well has increased by 950t. It also provides guidelines to the engineers with respect to refracturing design and commercial viability. In addition, this technology is not only suitable for vertical wells, but also for horizontal wells.

Multi-Fracture Growth Law for Temporary Plugging and Diversion Fracturing of Horizontal Well with Multiple Clusters in Shale Reservoir

“…Initially, the pipeline is filled with approximately 500 mL under a constant pressure of 1 MPa, followed by injection at a constant rate of 200 mL/min until a pressure drop occurs and cannot be re-pressured, indicating successful fracturing. Studies have shown that a combination of differentparticle-size temporary plugging agents can effectively increase the sealing pressure [23][24][25][26]. Therefore, the IFTP and ISTP stages use variable-viscosity slickwater with a viscosity of 5 mPa•s, which is supplemented with a combination of small-particle-size plugging agents (80-120 mesh + 20-80 mesh) and large-particle-size plugging agents (1-2 mm + 1-3 mm), respectively.…”

Experimental Investigation of the Growth Law of Multi-Fracture during Temporary Plugging Fracturing within a Stage of Multi-Cluster in a Horizontal Well

“…Temporary plugging agents composed of different particle size are often sent to plug the fracture near the well and promote the fracture diversion in the fracturing process, since the temporary plugging efficiency of multi-particle size combined temporary plugging agents are better than that of single particle size temporary plugging agents [30][31][32][33]. Four groups of rock specimens were designed for comparative experiments in order to study the influence of different particle size combinations of temporary plugging agents on the fracture propagation geometry in temporary plugging fracturing, respectively, 1#, 2#, 3#, and 4#.…”