Characterization of natural fractures in carbonate reservoirs to the resolution of well tests is reliable for major fracture corridors. These fracture corridors, intersecting or non-intersecting the wells, impact the well performance and the ultimate recovery in the field. Good transient-test data is the key to diagnosing fractures and their characteristics. When fractures exist between the wells, it requires some additional efforts in locating these with respect to the wells. To overcome this challenge we propose a new approach of building 3D, numerical models to diagnose and characterize the inter-well fracture corridors. In addition, these 3D multi-well, numerical models are to determine the location and the extent of fracture corridors by utilizing dynamic pressure-transient data. The innovative idea of bringing multiple wells to the models to consider interference of wells and fracture corridors makes the models robust. We have been able to identify the inter-well fracture corridors successfully in carbonate reservoirs by performing pressure-transient analyses on wells. By adjusting the inter-well locations of fracture corridors and the extents of these fracture corridors in the multi-well models, we try to achieve the best possible matches with the transient-pressure data. This integrated approach will provide essential input to 3D full- field reservoir models, and will lead to optimizing field management.

Sometimes electrical submersible pumps (ESPs) are deployed in oil wells to compensate for low reservoir pressures. Although such an artificial-lift mechanism dramatically boosts production rates, there are consequences on the quality of transient-pressure data in some cases. The paper presents the results of a thorough investigation of the behavior of pressure-transient data from horizontal wells equipped with ESPs in an oil field. Capturing the transient data without any distortion is important in estimating parameters of a horizontal well. This ensures establishment of all the important flow regimes on the log-log plot. But the early-time data suffers from distortion in buildup tests due to a very short period of hydrostatic balancing of fluids in the production string right after the ESPs are turned off. Drawdown data and rate transient analysis tools have been utilized to retrieve key well and reservoir information which might be missed in the early-time buildup data. Such integration is enabled by large sets of data from permanent downhole monitoring systems. Distortion of the early-time buildup data due to the falling liquid levels and some natural flow right after the ESPs are turned off for buildup tests consequently masks the early-time, vertical radial-flow regime. This distortion sometimes makes it impossible for unique estimates of the effective horizontal well length, the anisotropy ratio (vertical to horizontal permeability) and the damage skin. However, the empirical investigation shows that the early, vertical radial-flow regime develops in some drawdown tests with minor ESP effects. This drawdown data has been utilized to offset or reconstruct the flow regimes missed by the distorted early-time buildup data. In some cases, any low sampling frequency, low gauge resolution or lack of repeatability of the measured intake pressures at the ESP may hinder development of the early, vertical radial-flow regime in some drawdown tests. Note that a high sampling frequency and a high gauge resolution is required in capturing this flow regime. We have utilized rate-transient analyses to complement the pressure-transient analyses results whenever large data sets are available. The literature is devoid of any discussion on the challenges of interpreting the buildup tests on oil wells equipped with ESPs. This investigative paper with examples makes a comprehensive effort to understand such challenges. We have also shown ways to get around the problems and have provided reasonable interpretation of transient-test data.

A solid understanding of challenging reservoir complexities such as, naturally fractured "super-k" zones, layered systems, or, wellbore conditions such as, thermally induced mobility changes in the near wellbore region due to injection and uneven formation damage distribution across the wellbore, is essential for a successful development of carbonate reservoirs. These type of complexities play a major role for both reservoir fluid flow and well productivity. An efficient and holistic approach encompassing multiple data sources like image logs, production analysis logs, and pressure transient analysis (PTA) outcomes is of paramount importance in the characterization process of carbonate systems. In this paper illustrative examples showing different complexities, at reservoir level and also at well level, are presented in a systematic way to show the importance of pressure transient analysis (PTA) insights as a building block in the description process of these challenging reservoir features. Reconciling the differences between the static and dynamic data sources in each case was a crucial step to minimize the uncertainties encountered and to significantly broaden the dynamic understanding of these complex reservoir heterogeneities under a synergistic approach. Pressure buildups and falloffs data from multi-well groups, were incorporated and analyzed by advanced numerical models. The selected interpretation models were dependent on the reservoir and wellbore condition diagnosed from the pressure derivative plots. The analyses of wireline and large, real-time Intelligent Field data have provided key dynamic well parameters, such as permeability-thickness product (kh), productivity index and anisotropy ratio (kv/kh), that were critical input parameters in the characterization process of these complex reservoir systems.