K 6-3 was drilled in Kakkonda, northern Honshu Island by Tohoku Geothermal Energy Co., Ltd. as a production well for the Kakkonda No. 2 power plant; that will be operational in 1996. Initially in Kakkonda, about 70 wells with depths ranging from 1, 000 to 2, 000m depths were drilled and geothermal fluids were tapped from a tertiary formation. But recently 3 deeper wells were drilled into a pre-tertiary formation and neo-granitic rocks. These wells discovered a deeper promising reservoir. The planned depth of K6-3 was 2, 800m but it was deepened to 3, 000m when a fracture zone was found at 2, 764m. It took 180 days to drill from spud in to TD. This included 33 days for lost circulation treatments in the shallower depths and 27 days for 15 trajectory correction runs with downhole motors. Retrievable type MWD (ANADRILL SLIM-1), with a temperature limitation of 150°C, was first employed for the high temperature geothermal well at the depth range of 1, 531 to 2, 245m, where the formation is over 330°C. Twenty-seven MWD runs were recorded for both downhole motor drilling and rotary drilling. Total operating time was about 300 hours and total downtime was 13 hours; which was mainly due to battery parts failures. Two cooling towers and a 500kl cooling pit were used to cool the returned mud. These systems worked well, but the stator rubbers came off for the downhole motors used at about 2, 198m and 2, 245m depths. Below that depth, only rotary packed assemblies with long blades stabilizers were employed to keep the trajectory as straight as possible. Low content bentonite mulls with high temperature dispersant and lubricant were used as a drilling fluid. Various temperature data were taken, such as temperature logging at TD, logging at 2, 200m before running 95/8″ liner, mud temperature in and out of the well, mud circulation temperature recorded by MWD, and bottom hole temperature recorded by thermometers installed on top of the magnetic single shot tool. The following results were found: (a) Even if the formation temperature is 350°C drilling fluids can be cooled with proper cooling system and bottom hole circulation temperature (BHCT) can be kept about 80°C in a 121/4″ hole. (b) Even when pumping colder mud BHCT incre ased very much for the 81/2″ hole. This is maybe because of decreased pump rate for the 81/2″. (c) The BHCT decreased drastically while drilling with lost circulation. Acid fluids were expected for this well, so a duplex tieback casing was installed from surface to 400m depth.
In our previous papers, we have developed rapid and simple analytical methods of elements and minerals in oil reservoir rocks, for reservoir characterization and the solution of production troubles. Taking account of the localization of mineral or elements in rocks, rapid analysis of many samples were required. For elemental analysis, we used the EDX-FP (Energy Dispersive X-ray Fluorescence & Fundamental Parameter) methods, and improved analytical accuracy by spectrum matching method. For analysis of clay carbonate minerals, we used the DRS (Diffuse Reflectance IR Spectrometry). These analitycal methods were applied for real rock samples, and it is obvious that these methods were useful in many cases as follows. 1. By DRS methods, we can obtain the depth profile of clay minerals more rapidly and simply than XRD. 2. For acidizing operations, we can provide the typical elemental composition of target reservoir by EDX-FP methods. 3. By the combination of these methods, we can estimated the elements in each minerals. It is expected to obtain more chemical information of oil reservoir rocks by statistical methods.
The objective of this paper is to describe the importance concerning the conversion of high sulphur kerogens (type II-S) to petroleum. Those kerogens are known to be derived from siliceous and carbonate source rocks and to bigin the conversion even earlier, possibly due to the abundance of sulphur bonds compared with other types of kerogen (Orr, 1986). In general, however, it is difficult to make a direct comparison of the timing of oil generation among different kerogen types on the basis of geological data such as hydrocarbon ratio and/or vitrinite reflectance. Moreover, there has been a controversy about determining oil generation thresholds using the vitrinite reflectance (Ro) for different kerogen types. Consequently, in this paper, the timing of petroleum generation for different types of kerogen is examined from the standpoint of kinetic models as reported by Tissot and Ungerer (1990). However, until recently, most exploration geologists were not familiar enough with organic geochemistry to use kinetic models, and preferred the simplified model of Lopatin-Waples method (Waples, 1980) which assumed reaction rates to double for each 10°C increase. From the viewpoint of the above, in the first report, the chemical kinetic modelling of petroleum generation reported by many researchers is outlined briefly and then it is pointed out that TTI model (Lopatin-Waples method) has no theoretical basis and is not suitable for modelling oil generation based on the comparison of TTI with kinetic model of oil generation. In the second report, it is emphasized that high sulphur kerogen begins to generate hydrocarbons remarkably earlier than other kerogens do according to the kinetic model (Tissot and Ungerer, 1990) and that this phenomenon is important for the origin of immature or shallow depth oils and the exploration of those oils. Finally, it is suggested that oil from the high sulphur kerogen might be generated during diagenetic stage, if we consider the origin of high sulphur kerogen and try to apply the kinetic calculation to the organic matter in diagenetic stage.