Abstract
As an important energy replacement block in China, the tight conglomerate oilfields in the Mahu area are difficult to develop and are characterized by strong heterogeneity, large horizontal stress differences, and undeveloped natural fractures. However, new development processes including temporary blocking diversion and large section-multiple clusters have been implemented on the oilfields in the past few years. In 2020, two adjacent horizontal wells in the MD well area experienced a poor fracturing development effect compared with the earlier wells in this area. Analysis suggests that the main reasons are water sensitivity of the reservoir, insufficient fracturing scale, and/or interference from the adjacent old wells. To ameliorate the problem, this study presents an experimental study of multiple temporary plugging and refracturing technology in long horizontal well sections, in combination with electromagnetic and microseismic monitoring. Results from the study show a great difference between the two monitoring techniques, which is attributed to their different detection principles. Interestingly, the combination of the two approaches provides a greater performance than either approach alone. As the fracturing fluid flow diversion is based on temporary plugging diversion and electromagnetic monitoring of fracturing fluid is advantageous in temporary plugging diversion monitoring, both approaches require further research and development to address complex situations such as multiple temporary plugging and refracturing in long intervals of adjacent older wells.
Highlights
The tight conglomerate oilfield in the Mahu area is an important resource replacement block in China and is characterized by highly heterogeneous reservoir physical and mechanical properties, such as large horizontal stress and undeveloped natural fractures, which poses great challenges for the field development (Li et al, 2020)
The two monitoring technologies need to be further developed in tandem having in mind some questions such as 1) what are the differences in microseismic characteristics between an old fracture area in a refracturing process, a new fracture area in a secondary fracturing process, a diverted fracture area, and a low-aspirate channel area?, 2) Is the microseismic de-noising algorithm appropriate, and are there disturbances and inappropriate filters for these simultaneous events?, 3) Does continuous injection of the fracturing fluid/diverter cause continuous microseismic events in adjacent fracture network areas?, 4) What is the relationship between the amount of fracturing fluid accumulation and the intensity of microseismic events?
Electromagnetic monitoring provides a physical detection method to directly observe the dynamic changes of the fracturing fluid enrichment location in multiple temporary plugging diversion
Summary
The tight conglomerate oilfield in the Mahu area is an important resource replacement block in China and is characterized by highly heterogeneous reservoir physical and mechanical properties, such as large horizontal stress and undeveloped natural fractures, which poses great challenges for the field development (Li et al, 2020). The event point extended to well M7, and the pressure of well M7 rose to 25 MPa during fracturing At this stage, 1388 m3 liquid is injected with a fracturing pressure of 88MPa and shut-in pressure of 30 MPa. It can be observed that the temporary plugging was successful with an obvious time effect, and the signal of the old plugging area 2 was enhanced along with new crack openings in area 4. The microseismic events mainly occurred at the two wings of the perforation in stages 13 and 14, which were coincidental with the old fractures At this stage, 1,229.9 m3 liquid is injected with a fracturing pressure of 68 MPa and a shut-in pressure of 30 MPa. Successful temporary plugging is observed with an obvious time effect and enhanced signal for the old plugging areas 1 and 2. The water cut of well M2 rises sharply after well pressure, which validates the liquid enrichment area near the well trajectory observed by the electromagnetic monitoring method
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