Yufutsu Gas Field Research Articles

勇払油ガス田〜あけぼの地区におけるスルーチュービング改修作業

Japex did the workover operations in Yufutsu gas field, Hokkaido in 2004. It was an unique and challenging workover operations. The well had been suspended because more than 3,500m of 1.25in coiled tubing was left in 3.5in production tubing. This well had to be stimulated due to the damage of reservoir, so the coiled tubing must be retrieved prior to stimulation. The situation was very serious because of the narrow annulus of the string, so selection of the pipe and tool size were restricted, accordingly the yield strength of such macaroni pipe and tools were so weak. After an examination, the plan was made to retrieve the coiled tubing from inside of 3.5in production tubing by using 1.9in work tubing, thru-tubing fishing tool and slim-hole wireline tools. This operations were performed by drilling rig in case of contingency.Wireline chemical cutter was one of the key tools in our program. Unfortunately it was not working properly so we abandoned to use it and change the plan to swallow the coiled tubing with continuous overshot and 1.9in work tubing. Continuous overshot made an excellent progress and almost all the coiled tubing was retrieved from the well. Then the well was circulated and cleaned with brine, the operation was done in the budget.Stimulation was performed in April, 2005, as a result, productivity was improved substantially and this project was completed successfully.

油ガス田におけるＡＥ法によるフラクチャー計測の可能性

A small-scale hydraulic injection experiment was conducted in the Yufutsu gas field in October 2003, to see the feasibility of AE (acoustic emission) monitoring for the purpose of the fractured reservoir delineation. Although many success stories have been reported from the area of geothermal fields, none of the study in oil/gas reservoir has been done in Japan. This is the first experiment in oil/gas reservoirs in this country. We have succeeded in recording more than 450 of good quality AE signals by downhole sensors installed at 2, 700-2, 790m depths during the injection of 280 tons of brine solution into the depth interval 4, 412-4, 995m in the gas saturated reservoir. As the results of AE analysis, it becomes clear that the distribution of the AE events has close relationship with the distribution of pre-existing fractures along the well and that the shearing associated with AE events improves the injectivity of the injection well.The results of the field experiment were discussed through numerical simulations by using the SHIFT that simulates the shearing of fractures and relating permeability changes. The simulated results show a good matching in the pressure response and the AE activity, and provide us with useful understandings of the dynamics of the reservoir.

北海道の鉱物資源

This lecture introduces histories and present conditions of development of mineral resources in Hokkaido.The history of gold digging goes back to 12th century. But systematic development of mineral resources started from Meiji era especially for coal. Lyman's geological survey in this period established a foundation of mining industry in Hokkaido.Metal, non-metal and coal minings and oil development grew rapidly during the World War I. And metal, non-metal and coal minings reached their highest production during the World War II. But the mining industries started declining from mid-1950's. Especially severe decline took place in coal mining due to its high production cost.Activities of oil and gas exploration started increasing in 1970's according to MITI's exploratory drilling program as the fourth five-year-project. And Yufutsu gas field was found in 1989.Currently three metal mines, seventeen non-metal mines, eight oil/gas fields and eleven coal mines are working in Hokkaido. Zinc and limestone mines have large shares of production in Japan. Yufutsu gas field started production from 1996 for town gas used in Sapporo.Finally this lecture introduces new surveys for mineral resources in Hokkaido, because its potential is still high. And oil and gas development in Sakhalin is expected to give a great influence on Hokkaido.

勇払開発１０年のあゆみ

The Yufutsu Gas Field underlying in depths more than 4, 000 meters, locates in the vicinity of the Tomakomai industrial area, 50km south of Sapporo-city in Hokkaido, Japan. The field was discovered by the exploratory well “Minami-Yufutsu SK-1” in 1988 after years of exploiting activities of JAPEX.Exploration drilling in the southern part of Hokkaido had been continually carried out by JAPEX since 1961, in an attempt to find a promising hydrocarbon accumulation in the area. These efforts had, however, resulted in failure before the Minami-Yufutsu SK-1 well, because of production capability of each well that was not assessed to be commercially viable.Subsequent to the successful result in the Minami-Yufutsu well, a series of delineation wells was drilled, disclosing the essential information to evaluate the reservoir, and encouraging us to take further steps towards its development.Following an intensive study of examining the field from both technical and economic points of view, its development was officially announced in 1993. Production began in early 1996, supplying clean energy of natural gas to the local community.This field is quite distinctive among other gas fields worldwide in its type of reservoir formations, which are in combination of naturally fractured granite and conglomerate.Due to the type of reservoir formations, the depths underlying, and the reservoir fluids properties, that contain waxy oil of its pour point indicating 82°F, there were a number of difficulties in designing and executing both well construction and well completion operations.This report gives an overview of the technologies/solutions applied to develop the field during the past decade, and will help us foresee our business circumstances in the next decade.

北海道勇払地域におけるフラクチャー解析

This paper discusses the methodology for fracture detection and fracture porosity evaluation through core description, mud log and well logs, using data from Yufutsu gas field, Hokkaido, Japan. The youngest fracture group observed on core (System C) consists mainly of open fractures and roughly correlates with the conductive type fracture image on FMI. The remaining core fracture groups (System A and B) are filled by minerals and correlate with the resistive type fracture image. These results suggest that a substantial part of fracture pore space is associated with System C. The drill stem test results show that the most reliable fracture indications on mud log and conventional well logs are lost circulation while drilling, spiky peak of showing and abnormaly low values of RLLD. The values of φFMI and φRLLD-RLLS are low and nearly equal because both are probably close to the minimum fracture porosity. The trend of SPI (φD-φS) is similar to those of φFMI and φRLLD-RLLS, but the values of the former are several times larger than those of the latter. As above mentioned, the value of fracture porosity is various due to the difference of estimation formula and quantitative fracture porosity evaluation of the study area is still on the trial and error stage. So, further study will be needed for establishing more reliable method of fracture porosity evaluation.