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The radius of investigation (ROI) is an essential parameter in many reservoir engineering applications. Inconsistencies and ambiguities still exist between different ROI evaluation methods, especially for the dual-porosity (DP) system representing naturally fractured reservoirs. This paper revisited the impact of inter-porosity flow in the DP system and presented ROI equations in the early and late flow periods based on the Laplace space solution of the Warren-Root dual-porosity model. A new comprehensive ROI expression for the DP system is derived which accounts for both storativity ratio ( ω ) and inter-porosity flow coefficient ( λ ). The new method in this paper reveals that the log-log plot of ROI vs. time for DP models exhibits two parallel straight lines linked by a smooth transition curve. The distance of these two straight lines is dependent on ω , and ROI in the intermediate flow period is highly dependent on the value of λ. The new ROI equation for the DP system can degenerate to similar ROI formula for the single-porosity system in early and late flow periods. Comparison analysis of the new method with other approaches is conducted and the validation of the new method is realized by analytical and numerical matching. [ABSTRACT FROM AUTHOR]

Radius of investigation (ROI) is of great significance in well testing and reserve estimation. The studies on ROI over the past decades were mainly focusing on homogeneous reservoirs. In heterogeneous formations, such as composite reservoirs and fractured reservoirs, the problem remains unsolved. Few ROI evaluation methods for composite reservoirs have been validated and commonly accepted. This paper conducts extensive analytical and numerical analysis on the pressure propagation of composite reservoirs, analyzing the limitations and misunderstandings of previous methods on the evaluation of ROI. The pressure solution of a two-zone composite reservoir is presented in the Laplace domain and is used to analyze the impact of heterogeneity parameters on pressure transient propagation and the evaluation of radius of investigation. A new ROI formula for composite reservoirs is proposed, which is in great agreement with the analytical solution. The study reveals that the inner zone of a composite reservoir cannot be treated as homogeneous when the pressure front approaches the interface of the two zones with high heterogeneity. A large mobility ratio will slow pressure propagation in composite reservoirs, while a low storativity ratio will increase the value of ROI. Reservoir simulation and real case studies are used to demonstrate the findings of the analytical study. The new study sheds insights into the pressure propagation and eases the calculation of ROI in composite reservoirs. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive overview of Deep Transient Testing (DTT), a cutting-edge technique for reservoir characterization that has revolutionized the oil and gas industry. The main aim of DTT is to characterize the reservoir with a deeper radius of investigation. The optimization of the radius of investigation with the DTT approach is studied in detail. Reveal is a commercial numerical simulation application used to simulate the DTT process and evaluate the pressure wave analysis in the porous media. The main aim of the simulation is to understand the impact of the reservoir quality on the pressure response and use it to address the noise-to-pule ratio, which is a determinantal parameter in testing duration. The tested wells with the DTT tool show that measured well productivity can deliver the minimum commercial rate. The has been delivered within 2 days compared to the potential test time of 21 days which saved the 19 rig days and contributed to CO2 emission reduction of (gas flaring 1340 + rig emission 600) 1940 Metric tons equivalent to 421 cars emission in a year. However, DTT also presents certain limitations, such as the requirement for specialized equipment and expertise, as well as the potential for formation damage during testing. This study provides a detailed description of the DTT technique, encompassing its history, theory, and practical applications. Furthermore, it discusses the benefits and limitations of DTT and presents case studies to illustrate its effectiveness across various reservoir types. Overall, this study serves as a valuable resource for reservoir engineers, geologists, and other professionals involved in the exploration and production of oil and gas.

Many studies on the pressure propagation in porous media show that the relationship between the square of the radius of investigation and the producing time of a well is linear. The linear relationship is the pressure propagation equation (or pressure equation). However, these studies do not arrive at the same constant coefficient representing the linear relationship. The purpose of this study is to find the constant coefficient for the pressure propagation equation. The constant coefficient from this study is derived from analyzing pressure transient behavior and observing the boundary effect time (the starting time of wellbore pressure affected by the reservoir boundary). The results show that the constant coefficient in the pressure equation, i.e., the linear constant between the square of dimensionless radius of investigation and the dimensionless producing time is 17.82. [ABSTRACT FROM AUTHOR]

• The radius of investigation during the recovery phase of pumping tests is analyzed. • Exact (semi-analytical) and approximate (fully analytical) solutions are derived. • The radius of investigation can be significantly larger than at the end of pumping. • The maximum radius of investigation can be reached long after pumping is stopped. • Pumping rate and duration, and apparent measurement resolution are key parameters. Pumping tests are routinely performed to characterize aquifers. In particular, recovery tests involve analyzing the residual drawdown after the termination of pumping. Evaluating the radius of investigation of pumping tests is important for test design and interpretation. However, the radius of investigation during the recovery phase has rarely been discussed in the literature. Here, we derive exact (semi-analytical) and approximate (fully analytical) solutions for the radius of investigation during the recovery phase, and present a sensitivity analysis for typical parameter values. During recovery, the radius of investigation shows non-monotonic behavior: it first increases, then decreases, and eventually vanishes. The maximum radius can be up to five times larger than that at the end of the pumping phase in the investigated range of parameter values. However, the conditions yielding a large radius of investigation are such that the time at which the maximum occurs is relatively large: up to one hundred times the pumping duration, depending on the parameters. Thus, in practice, one may need to find a compromise between the size of the investigated area and the time required for the test. In addition to the aquifer parameters, we observe that the pumping rate and duration, and the apparent measurement resolution are key parameters controlling the radius of investigation during recovery. Finally, the approach is applied to a field example. This study provides fundamental insight on the radius of investigation of recovery tests as well as practical solutions, thereby facilitating the design and interpretation of recovery tests in practice. [ABSTRACT FROM AUTHOR]