Lun Zhao

A New Method of Calculating Recovery of Waterflooding Reservoir by Using Production Rate

Development characteristics of oil field during production-decreasing stage were analyzed in this paper. The ultimate recovery factor can be determined at a limit of oil production rate by investigating the relationship between production rate and recovery percent. Some physical conditions were given. Based on the mass conservation principal and seepage mechanics method, it was found that the recovery degree varies versus production rate linearly. The model prediction using the actual data of west Ng63+4 oil strata in Gudong 7 region, a reservoir in Shengli oilfield of China, was performed. The results demonstrated that the linear model had well estimation of the recoverable recovery of oil fields which were at the later period of high water cut stage.

Influence of Sandstone Architecture on Waterflooding Characteristics in Common Heavy Oil Reservoir

Taking common heavy oil reservoir as an example, we characterized spatial structure characteristics of delta front and analyzed waterflooding characteristics of underwater distributary channel sand, mouth bar sand, and beach bar sand, finally cleared the fact that sandstone architecture has influence on waterflooding characteristics in common heavy oil reservoir. The research results show that spatial structure characteristics of delta front are complicated: vertically, single sand bodies have independent, superposed, and cutting-stacked contacts with each other. Sandstone architecture has great influence on waterflooding development: Underwater distributary channel sand has positive rhythm characteristics, and mouth bar sand has weak inverted rhythm characteristics with low permeability contrast value as well as beach bar sand has homogeneous rhythm characteristics. Therefore, at the process of waterflooding development, because of the influence of gravity and high viscosity of heavy oil, the bottom part of underwater distributary channel and the bottom part of most mouth bar sands are priorly waterflooded, while beach bar sand is waterflooded uniformly; long-term waterflooding and high viscosity characteristics of heavy oil will lead to formation of dominant water flowing channel in sand inside and cause remaining oil accumulate at the top of sands, which are the main target for late tapping.

Advanced mathematical model for reservoir heat efficiency with liquid in steam-injection wellbore

ABSTRACT The accurate determination of reservoir heat efficiency of steam injection in heavy oil reservoirs is very important for heating radius calculation and production dynamic prediction. In conventional calculation methods of reservoir heat efficiency, the steam-injection wellbore is assumed as taking steam over the entire height. In fact, a liquid level in steam-injection wellbore is a very significant observation with respect to the steam override. Aiming at the actual situation that the steam-injection wellbore always has a liquid level, combined with the formation temperature distribution, the new mathematical model for reservoir heat efficiency with the consideration of liquid in steam-injection wellbore was established based on the Van Lookeren steam override theory and the energy conservation principle. The established mathematical model was used to calculate and analyze the reservoir heat efficiency of steam injection in heavy oil reservoirs. The results show that because the new mathematical model considers the liquid in the steam-injection wellbore, the predicted results are more reasonable, thus verifying the correctness of the new model. According to the influential factors analysis based on the new model, it is observed that although increasing the steam quality can effectively increase the steam-taking degree of the steam-injection wellbore, it has limited impact on reservoir heat efficiency. Moreover, the larger the steam-injection rate, the higher the steam-taking degree and reservoir heat efficiency. The reservoir heat efficiency decreases with the pay-zone thickness when the steam-injection wellbore has liquid.

A New Mathematical Model For Heat Radius of Cyclic Superheated Steam Stimulation with Horizontal Wellbore

When superheated steam flows along the horizontal wellbore, it may change to saturated steam at some point of the wellbore. In this paper, to accurately predict the heat radius of cyclic superheated steam stimulation with horizontal wellbore, the distribution of thermophysical properties of superheated steam along the horizontal wellbore is considered. The heating process is divided into 4 stages for superheated steam and 3 stages for saturated steam when the phase change undergoes in the wellbore. On this basis, the mathematical model for heat radius of cyclic superheated steam stimulation with horizontal wellbore was established according to energy conservation principle and Laplace transformation method. The calculation result of the new mathematical model is in good agreement with that of the numerical simulation (CMG STARS) for the same parameters from a specific heavy oil reservoir, which verified the correctness of the new mathematical model. The effect of degree of superheat and the cycle of stimulation are analyzed in detail after the new mathematical model is validated. The results show that the heat radius of superheated zone, steam zone, and hot fluid zone all decrease with horizontal well length and increase with the cycle of stimulation. The higher the degree of superheat is, the farther from the heel of the horizontal wellbore the phase change undergoes. Besides, the radius of superheated zone, steam zone, and hot fluid zone increases with the degree of superheat, but the value increases little at steam zone and hot fluid zone.

Foamy oil properties and horizontal well inflow performance relationship under solution gas drive

ABSTRACT In this study, we modified the foamy oil fluid property model by defining the coalescence rate constant to account for the fraction of entrained gas in the oil phase. The modified model was verified by matching the calculated results with experimental data. Then, the horizontal well inflow performance of foamy heavy oil reservoirs was calculated by incorporating the modified fluid properties into the horizontal well flow rate equation at pseudo-steady state. In addition, the horizontal well inflow performance of foamy oil under solution gas drive and the corresponding conventional oil was compared. The results show that the foamy oil fluid properties calculated by the modified fluid property model are consistent with the experimental results, thus verifying the correctness of the model. Comparing the horizontal well inflow performance of foamy oil and conventional oil, it shows that when the average reservoir pressure is between bubble point pressure and pseudo-bubble point pressure, the flow rate of foamy oil is higher than that of the conventional oil. When the average reservoir pressure drops below the pseudo-bubble point pressure, the flow rate of foamy oil is close to that of the conventional oil. Foamy efficiency, defined as the ratio of the difference between the flow rate of foamy oil and conventional oil to the conventional oil flow rate, has the biggest value, about 15%, close to the pseudo-bubble point.

Temperature distribution of fluids in a two-section two-phase closed thermosyphon wellbore

Compared with a conventional single section two-phase closed thermosyphon (TPCT) wellbore, a two-section TPCT wellbore has better heat transfer performance, which may improve the temperature distribution of fluid in wellbores, increase the temperature of fluid in wellheads and even more effectively reduce the failure rate of conventional TPCT wellbores. Heat transfer performance of two-section TPCT wellbores is affected by working medium, combination mode and oil flow rate. Different working media are introduced into the upper and lower TPCTs, which may achieve a better match between the working medium and the temperature field in the wellbores. Interdependence exists between the combination mode and the flow rate of the oil, which affects the heat transfer performance of a two-section TPCT wellbore. The experimental results show that a two-section TPCT wellbore, with equal upper and lower TPCTs respectively filled with Freon and methanol, has the best heat transfer performance when the oil flow rate is 200 L/h.

Nonlinear Behavior and Characterization of Flow through Preferential Seepage Channels

The Darcy linear equation has been widely used to describe the fluid flow in porous media. It is inaccurately used to describe the flow through preferential flowing paths which exert important influence on the performance of waterflooding reservoir. In this paper, the following two problems have been studied: (1) flow law in preferential flowing paths generated by water flooding; (2) sound nonlinear mathematical model considering special internal and external boundary conditions. The greater the permeability in porous medium becomes, the easier fluid can flow. Meanwhile the flow mechanism would change correspondingly as well. Exact solution of the nonlinear model is obtained analytically by integration. It is shown that in preferential flowing channels the flow velocity and the pressure gradient are a nonlinear relationship which is different from the traditional Darcy theory described as a straight line. Finally, the seepage characteristics of nonlinear flow and its influence are determined by analyzing the pressure gradient curve and velocity distribution between the observation point and the target well. Keywords: Preferential flowing paths; Non-linear model; Forchheimer equation; Integration method; Pressure gradient.

Gas Cap and Oil Rim Collaborative Development Technique Policy of Carbonate Reservoir with Condensate Gas Cap

Zhanazhol oilfield is a large-scale complicated carbonated oil and gas field , Гnorth is the main oil and gas reservoirs of the oil field, The gas cap index is 0.38, the gas cap on a high condensate content. Reservoir development for nearly 25 years, exploitation in the past only to oil ring. Due to insufficient water injection in early age, the oil ring pressure dropped substantially, and the formation pressure to maintain the level of only 58%. For oil and gas reservoirs with a condensate gas cap, gas cap and oil ring at the same pressure system, with the decline in the pressure of the oil ring, the gas cap continue to spread to the oil region, while there are a large number of condensate oil anti-condensate from the gas cap, which loss into the formation. In this paper, the authors consider the characteristics of the oil and gas reservoirs and research the technique policy of collaborative development, These are all in order to solve technical problems, which is keep the pressure balance between the gas cap and oil ring during collaborative development. Not only provide technical to support the rational and efficient development of the Г North oil and gas reservoirs, but also provide a stable source for natural gas pipeline from Kazakhstan to China.

Productivity Analysis of Transverse Horizontal Well Commingling in Stripped Gas Reservoir with Bottom Water

Banded gas reservoir with bottom water is a typical gas reservoir. Based on the development characteristics of formation, the further study on commingling production by transverse horizontal well is done, and also combined with seepage theory including the Green function, Duhamel method etc. the dimensionless definitions of relative parameter are given. Whats more, the derivation and formula of production can be achieved respectively under the constant pressure condition and constant production condition. Meanwhile, take commingling production with three banded gas layers for example. Whether the initial pseudo pressure for these layers are equal or not, in both of these cases, the variation curve of gas productivity under the constant pressure and constant rate conditions is described separately. And the law of variation of gas flow backward for some layer when the physical properties of these layers are significantly different.

Optimizing Well Spacing Using Srkachef Relational Expression

With the remarkable improvement in recognition concerning the feature of the reservoir, a comprehensive adjustment is required to be made during the process of field development. Among currently prevalent methods, well pattern thickening is regarded as the most effective way to maintain or boost the oil productivity. However, to avoid the consequent high development cost of this method, optimizing a reasonable well spacing becomes a necessity to ensure a desirable effect of exploitation as well as an advanced level of economic effectiveness. In this paper, the author sets Zhanazhol Oilfield as an example and uses Srkachef relational expression to provide an accurate method, in which gives a detailed illustration about optimizing economic limit well spacing and economic optimal well spacing in different thickness reservoirs. Given its favorable adaptability, this method will become a valuable reference for the oilfield development in relation to well pattern deployment and thickening in late period.