The utility of horizontal well in Kubiki oil field has been confirmed through the production performance of the two horizontal wells recently completed in this field. However, the production forecast based on the Joshi's solution does not match the actual. Two possible reasons are (1) the uncertainty of several parameters required for the forecast and (2) the ambiguously determined drainage area. To improve the quality of forecast, these uncertain parameters were examined through pressure analyses and the full-field simulation model was used. The resultant prediction is in good agreement with the actual production performance.
A case study was performed on the interaction between the flow behavior in a horizontal wellbore and the fluid influx from a heterogeneous reservoir. This has been recognized as one of the most important, yet unsolved problems in pertoleum engineering. Field data such as fluid influx distribution from the reservoir as well as pressure and fluid density distributions were acquired along a horizontal wellbore named “Yurihara SK-15” at the Yurihara Oil and Gas Field in Akita Prefecture, Japan. A mechanistic model POPHOZN was used as a tool to discuss key parameters affecting the steady-state production behavior of the horizontal well. The analysis of the production logging data demonstrated that POPHOZN could be applied for field application. The followings have been conducted as part of the present study on the analysis of flow behavior due to confluent fluid flux along a horizontal wellbore: (1) Field data such as fluid influx from the reservoir, pressure and fluid density distributions along a horizontal wellbore was successfully acquired by running a spinner flow meter and a densitometer with coiled tubings at the Yurihara Oil and Gas Field. (2) It was found that the gas-oil two-phase flow occurred in the horizontal section due to saturated reservoir conditions. The characteristics of the two-phase flow could be reasonably accounted for calculating pressure drop and fluid density distribution in the horizontal wellbore by the model POPHOZN. (3) The analysis of the production logging data demonstrated that the overall performance of the proposed model POPHOZN successfully simulated the interaction between the heterogeneous reservoir and the horizontal well configuration, and the flow hydrodynamics along horizontal wellbore could be physically expressed.
In the reservoir which contains randomly distributed impermeable shale, the shale density and the size of each shale affect the production performance of a horizontal well. In general, the oil recovery by water injection decreases with the increase of shale density and the shale correlation length. On the other hand, for the reservoir which has a bottom water, shale is considered to act as a barrier to the water encroachment, and the high shale density and large shale correlation length keep the oil production rate high. For the practical reservoir simulation, not the explicit reservoir model, which is the realization describing in detail all the shale position and size, but the implicit reservoir model, which is a homogeneous and anisotropic reservoir model characterized by the effective vertical permeability, is in use. In this case, the implicit model should be the one that reproduces the production performance of the corresponding explicit model correctly. In this study, three methods to construct the implicit model from the realizations which contain random shale ditribution are compared for both water injection and bottom water drive cases.
Recent interests for source rocks of oil are focused on the source rock potential of coal. On the van Krevelen diagram, coals which were collected from coal mines in Japan (Fig. 1) show higher H/C atomic ratio than that of the Type III (vitrinite) evolution path (Fig. 2). However petrographic compositions of main coal seam at the Taiheiyo Coal Mine show that they consist of more than 90% of vitrinite and a few percent of exinite and inertinite each (Fig. 3). Degradinite, which is a maceral of vitrinite group and used only in Japan, varies from 10 to 60% in content (Fig. 4) and has good correlation with H/C and O/C atomic ratios (Fig. 5, 6). This relation is also recognized at the Ikeshima Coal Mine (Fig. 7, 8). H/C and O/C ratios of pure degradinite are estimated from regression equations among the degradinite contents, H/C and O/C ratios within the Taiheiyo and Ikeshima coals. Estimations of the pure degradinite are plotted on the Type II kerogen evolution path (Fig. 9). Japanese Tertiary coals are rich in exinite group on the assumption that degradinite is included in exinite group. Based on ultimate analysis data for Cenozoic, Mesozoic and Paleozoic coals from Japan, China, Indonesia, Australia and USA, they are plotted several independent areas on the van Krevelen diagram (Fig. 10). Cenozoic coals from Japan, China and Indonesia suggest high H/C ratios than Mesozoic and Paleozoic coals of China and Australia. From the view point of oil generation, it is inferred that the Tertiary coals have higher potential than Mesozoic ones. Actually the geologic age of major oil fields where their source rocks are assumed to coal is limited to the Tertiary period.
The nonlinear regression algorithms used in this study perform a minimization of an objective function formed by the sum of the squares of differences between the data and the model values. This constitutes a typical nonlinear least-squares problem. Penalty functions are also used to restrict the domain of the parameters within consistent regions. In an application of the nonlinear regression, it is important to quantify the degree of confidence that can be associated with the estimated model parameter values. Confidence intervals are used to know how well the model parameters were determined. As a result, the Gauss-Cholesky method with penalty functions calculated efficiently relative permeabilities from unsteady state coreflooding experimental data.