Hydraulic fracturing using heavy brine was conducted to stimulate the deeper part of the completion interval in the naturally fractured reservoir, Yufutsu Japan. The microseismic monitoring and the temperature surveys showed that the deeper part was stimulated effectively as expected. The Yufutsu oil and gas reservoir is seated at around 4 km depth in the Southern Ishikari Plain, central Hokkaido, in northern Japan is known as a basement fractured reservoir. The water frac inducing shear dilation is one of the effective stimulation methods for the fractured reservoir. However it is difficult to stimulate the bottom part of the vertically long completion interval with seawater or slick water because the gradient of the fracture closure stress (that is typically 0.6–0.7 psi/ft, equivalent mud weight 1.4–1.6 sg) is commonly larger than that of the injection fluid. The heavy brine (CaCl2/CaBr2 brine 1.8 sg) realizes a pressure gradient larger than the fracture closure stress gradient that can stimulate deeper zone effectively. The numerical prediction using "SHIFT" simulator shows consistent results with the above-mentioned considerations. SHIFT simulates shearing of fractures and related permeability changes in a dynamic process by coupling analyses of the fluid flow and the shear dilation along fractures. The target well has a long completed interval of 700 m. The deeper part of this well showed poor productivity due to a damage of lost circulation materials. The fracturing operation using the 1.8 sg CaCl2/CaBr2 brine was conducted with the objective to stimulate the damaged zones. About 200kL of heavy brine was injected. The microseismic array sensor was installed in the adjacent well to monitor the stimulation during the injection. Approximately a thousand microseismic events were observed during the injection. The location of the microseismic events showed that the deeper part was stimulated effectively. A temperature survey conducted after the stimulation revealed the new production zones appeared on the temperature profiles as anomalies which had not been seen before. The AOFC of the well increased by a factor of 1.5. Introduction The Yufutsu Gas Field is a naturally fractured reservoir located in the southern Ishikari Plain, central Hokkaido, in northern Japan. The reservoir depth ranges from about 4,000 to 5,000 m and is comprised of Cretaceous granite overlain by Eocene conglomerate (Kurita et al., 2000). Productivities of more than a dozen wells drilled into the reservoir vary from none to high (Tezuka, 2002). This is considered to be caused by the strong heterogeneity of the fracture distribution. High productive wells have a tendency to have massive lost circulations during the drilling and/or widely opened fractures detected by the borehole images. Although this fracturing target well had the good signs such as a massive lost circulation and a wide open fracture, the result of the flow test did not show the high productivity. Some fluid flowing zones are found around the shaldeeper completion interval from the temperature survey, but the equipment tagged above the depth of the widely opened fracture because of the settlement of LCM (lost circulation material) and barite. The coiled tubing ran to confirm that the LCM and barite do not settle tightly at the bottom part of the borehole. Therefore, the squeezed LCM and barite into the fractures is determined to cause the poor productivity of the hopefully fractures occurred the massive lost circulation.
JACOS’ Hangingstone Demonstration Project has been in operation since 1999. The company has used the 10,000 bbl/D facility as a foundation for learning and refining SAGD processes and operations. The 24 operational well pairs, with 15 years of production has provided valuable insight into the performance of different liner completion types and operational control mechanisms. Data from the Demo project has provided the basis for a liner test strategy and liner design for application at JACOS’ Phase 1 Hangingstone Expansion project. First steam is expected in late 2016. All of the 24 operating well pairs at the Demo project have concentric tubular designs, but varying liner completion types. One well pair is completed with MeshRiteTM, 13 well pairs with wire wrap screens and 10 well pairs are completed with slotted liners of varying slot sizes. With a relatively strong surveillance program, the flow distribution (inflow), subcool control, hydraulics and operability for each of the well pairs were carefully analyzed. The performance of wells with MeshRite, wire wrap screen and slotted liners will be presented. The analysis provided insight into what was successful in the field and provided a strong basis for the test design. As part of the expansion project, field performance data from the six phases of the Demo project, coupled with particle size analysis, flow testing and thermal performance analysis, guided JACOS to select slotted liners for all injector wells. For the producers, 27 wellbores were completed with wire wrap screens and five wellbores with MeshRite liners, for a total of 32 well pairs. This comprehensive study incorporated field learnings, operational successes, and a comparison between the flow test observations and field observations. Finite element analysis and specialized drilling mud contributed to liner installation success for the Hangingstone Expansion.
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