There are two kinds of folds in Nishiyama oil field. One is box type and the other similar type fold. Principal stress distribution studied by conjugate faults analysis indicates that the lateral compressional stress, approximately NW-SE in direction is responsible for the formation of main structural features in this oil field. This NW-SE stress is believed to form the similar fold in southeasten side of the field (Nagamine anticline). On the other hand, in central area (Ushirodani anticline), the rocks were domed up by comparatively shallow formations. Although this conclusion is presented tentatively, it is well consistent to the result of Link's model experimentation.
Drilling ability of rotary cone bits were measured experimentally at atmospheric pressure. A laboratory drilling equipment used in this study could measure accurately load to rock, torque of a bit and displacement of a bit. When a bit rotated, there occurred the vertical vibration caused by movement of each tooth of cones of the bit. This vertical vibration of a bit produced variations in torque of a bit and load to rock and also in instantaneous drilling rate. Analyses of these variations measured by this equipment would be used to understand the accurate drilling ability of rotary bits.
The equations for the penetration rate reported by many researcher are applicable only under the condition of the adequate hydraulic action, i.e. clean bottom hole condition. But field drilling practices are in many case under the incomplete hydraulic condition. It is quite important to understand quantitatively the effects of hydraulics on the rock bit performance. The effects of hydraulics have been investigated from two standpoints: one is the maximum penetration rate attained under the adequate hydraulic action, other is the behavior of the penetration rate under the condition of the incomplete hydraulics. By drilling experiments by 11/4 in. two-cone microbits, three basic equations have been derived to describe the penetration trate in any hydraulic condition. (1) The equation for a performance line. This was proposed by Bingham (1964-65). This is applicable under the complete hydraulic action. (2) The equation for a branch-off-point penetration rate. When bit weight is increased with hydaulics maintained at the same level, the penetration rate branches off at a specific point on the performance line corresponding to the hydraulics level. Then, the penetration rate at the branch-off point is able to he used as a measure of the hydraulics effect. The relationship between them is affected by the properties of rock. When that relationship is obtained, it could be used to estimate the branch-off-point penetration rate for any level of hydraulics. (3) The equation for a relative penetration rate. The relative penetration rate and the relative bit weight are defined as follows: the relative penetration rate=R/R0 R=penetration rate under the incomplete hydraulic condition R0=penetration rate calculated by the equation for the performance line at the same bit weight and rotary speed, the relative bit weight=(W-Wc)/(Wb-Wc) W=bit weight Wb=bit weight at the branch-off point Wc=performance-line intercept. By using these quantities the relationship between the penetration rate and the bit weight is described by a single equation, i.e. the equation for the relative peneeration rate which is not affected by rotary speed, hydraulics and properties of rock. The characteristics of the bit design and wearing, if any, are only factors that affect the form of the equation. A tentative equation for the relative penetration rate has been obtained by rearranging the Thompsom's field data (1953). That is This equation would be applicable for analyzing and estimating the performance of any soft-type three-cone rock bit under the condition of the incomplete hydraulics.
(1) For seismic reflection method, we have made a study of noise in the area where the noise, what is called ground roll, is quite dominant. As the results, it becomes possible for us to clarify the subsurface structures up to around 4, 000 meters by controling the above noise with use of a well designed T-offset, in-line-offset, etc., because the noise was still more dominant than signal even by applying conventional pattern shooting, group setting of geophones and CDP (common depth point). (2) The practical applications of analog data processing system and Laser Scan to seismic exploration have given us a good support to interpret the deep and the complicated subsurface structures, and synthesized seismogram made from sonic log has improved our interpretative techniques to grasp the state of oil reservoir, As we also have recently been introducing the digital techniques into our seismic exploration system, we are to some extent able to solve such hard problems as attenuations of water reverberation and other noises which require quite elaborate processes based on deconvolution principles, and which however contribute much to grasp the deep subsurface structures. (3) The application of electronic digital computer to the analytical routines of gravimetric or magnetic explorations has been to obtain good results as well. With the computer we have energetically put into practice to compute gravimetric basement from gravimetric anomaly map and to compose profile on gravimetric or magnetic basement from respective profile, which is, we believe, powerful means to synthetically interpret the deep subsurface structures together with the informations from seismic explorations and from wells.
Abstract In this paper, the problemes on the magnetic modelling of geological structure and the reduction of magnetic dato are mainly treated. (1) The magnetic compartment in the basement complex, uplift and/or Subsidence of the base ment surface, the sills and the intrusives in the sediment are the cansative bodies of the magnetic anomalies, but the flow of volcanic rock overlaying the basement eomplex also plays an important role as magnetic basement, especially in Japanese oil-bearing pasin. (2) The use of high seusitivity ground magnetometer for reduction of diurnal effect could save much time in compilation procedure, but the limitation of this method should be taken into eareful consideration. After the discussion of these problemes, the example of the survey result in central Kambara plain is also discribed.
This paper outlines the subsurface geoloy of Niigata Plain by describing the characteristics of several tectonic provinces from north to south. In this way the history is developed chronologically and the methods used in preparing maps of underground conditions are illustrated. Niigata plain has recently become the most active exploration and development area in Japan. Extensive areal magnetic and advanced seismic surveys were carried out under the cooperation of several oil companies and direction of government agencies. Considerable number of exploratory wells have been drilled onshore and offshore directing the deeper and deeper formations. Comprehensive basin studies and compilation completed the preliminary investigations. The sedimentary basin of Niigata plain has been the scene of depositional cycles. A biostratigraphic subdivision is introduced for this basin subsurface comprising Haizume, Nishiyama, Hamatsuda, Shiiya, Teradomari, Nanatani and “Lowey Tertiary” formations. Three major Tertiary tectonic basins adjoin in northeast-southwest alignment in Niigata plain: Kita-Kambara, Nishi & Naka-Kambara and Nagaoka provinces. The general alignment of these provinces resulted from remarkable volcanisms across the generally east-west early tertiary volcanic trend of this basin. Potential petroleum traps of following types occur: tectonic fold ings, stratigraphic pinchouts, underblock structures and synchronous highs. Statistics, theory and field examples verify the important role of source beds for the underlying reservoirs. As the reservoir depth becomes deeper, the specific gravity of oil becomes lower. Relationship between depth and oil gravity however are different for reservoirs of each fields. The factor that cause the oil, condensate and gas variations must be related closely to lithologic character and formation-water chemistry of source beds.