A previously developed transient cuttings transport model using a two-layer model was modified to enable more practical simulation over the whole trajectory of a directional well. Two-layer model is usually used to describe solid-liquid two-phase flow in pipes in which cuttings bed is formed and the boundary between layers can be clearly recognized. In this study, two-layer model was extended to apply to describing cuttings transport behavior in relatively low hole inclination angles ranging from vertical to about 55 degrees, in which continuous cuttings bed was unlikely formed. Of the constitutive equations used, cuttings re-entrainment rate was re-formulated as a function of hole inclination angle and was corrected to match experimental results. To evaluate the modified model, field scale simulation on cuttings transport was carried out for a simple horizontal well. Simulation results showed that the modified model could successfully demonstrate transient behavior of cuttings transport over the whole trajectory of the well.
The aim of this study is to construct database of interpretation templates by synthesizing the seismic responses on the complex geologic structures reproduced by scaled analogue modeling. We combine such “analogue geological modeling” and “seismic modeling” to obtain clear seismic responses of complex geological structures. The procedure starts with an “analogue geological modeling” that uses granular materials to reproduce a three-dimensional geological model of thrust-and-fold belt type of deformation. Then the detailed digital structural geometry is reconstructed by digitizing the stratigraphic boundaries of the model sections. The 3D geometry is then used to execute “seismic modeling”, and the synthetic seismic record is obtained. The complex wave field recognized in the synthetic seismic sections shows the influence of the three-dimensional structure. Seismic data generated by the modeling are processed with 2D migration technique to make depth images. These sections can be adopted for investigation of the interpretation pitfall by comparing inline and cross line data sets. The features of the synthetic seismic sections are commonly observed on the actual seismic profiles at the Nankai Trough area. This fact suggests that the analogue model experiments are valid and our approach is effective. We are going to apply this approach to other geological structures, and construct data base of templates that can be used for the interpretation work in the future. Such database will help improving efficiency of petroleum explorations, which will be carried out in more and more complex geology.
Miocene hydrothermal activity resulted in the formation of the gas reservoir pore systems of the Nanatani Formation rhyolite lava in the Katagai gas field, Nagaoka area, Niigata Prefecture, Japan. Based on bulk chemical composition, and XRD and EDS analysis of drill core and cuttings, hydrothermal alteration zones of rhyolitic rocks are divided into the albite (RA), illite (RS), and chlorite (RC) zones. The RA zone is characterized by three types of pore spaces ; one is primary pore spaces, interstitial pore spaces between euhedral albite crystals, and the other leached pore spaces resulted from dissolution of albite which are associated with a small amount of chamosite and monazite. Hydrothermal solution containing dissolved cation (K, Al, Fe, Mg, etc.) leached from the RA zone had migrated to the surrounding rocks, and formed the RS zone. In the RS zone, illite, quartz and carbonate minerals are filled in pore spaces and along fractures, with lesser amount of micro-sized pore spaces. Almost all pore spaces of the chlorite zone, hosted by rhyolite (RC zone) and basalt, are filled with chlorite and other altered minerals. δ34S data of pyrite from Miocene mudstone, rhyolite and basalt show the mixing of magmatic sulfur and reduced sulfur from mudstone or basement rocks during the formation of the chlorite-illite subzones and the chlorite-pyrite subzone of the chlorite zone. Main contribution for gas reservoirs in the Katagai gas field is the interstitial pore spaces between euhedral albite crystals in the early stage, and the leached pore system derived from albite dissolution in the next stage. These pore spaces are filled with clay minerals and other altered minerals in hydrothermal system.