Real-Time Integrated LWD Formation Evaluation to Maximize Injectivity

The main objective was to drill a power water horizontal injector within the sweet spot of a thin fractured and heterogeneous reservoir to achieve pressure stabilization in this producing field and an optimized sweep at the bottom of reservoir to maximize and prolong production. A traditional triple-combo logging while drilling (LWD) portfolio cannot fulfill these challenging reservoir navigation and formation evaluation (FE) objectives simultaneously because of the limited number of measurements. Hence, a more holistic approach is required to optimize the well placement via the integration of real-time LWD FE measurements to maximize the injectivity. An integrated LWD assembly was utilized and offset well FE data were studied to select the best zone for well placement to provide the best injectivity and production of the remaining oil towards the base of the reservoir. Extensive pre-well modeling was performed, based on offset well data with multiple scenarios reviewed to cover all eventualities. Another challenge was to place the wellbore in a relatively low resistive zone (water wet) in contrast to normal development wells where the wellbore is navigated in high resistive hydrocarbon bearing zones, so conventional distance to bed boundary mapping methodology was not applicable. To overcome this challenge; advanced Multi Component (MC) While Drilling resistivity inversion was proposed in conjunction with deep azimuthal resistivity technology. The benefit of this technique is in providing the resistivity of each layer within the depth of detection along with thickness and dip of each layer. Resistivity inversion results were correlated with nuclear magnetic resonance (NMR) porosity and volumetric data to identify the best zone for well placement. As MC inversion was able to map multiple layers within ~7 ft radius depth of detection, changing thicknesses and dip of each layer; the geosteering team was able to make proactive recommendations based on the inversion results. These proactive trajectory adjustments resulted in maintaining the wellbore within a thin target zone (1-3 ft in thickness) also confirmed by NMR and Formation Testing Service (FTS) in real-time, achieving excellent net-to-gross, which otherwise would not have been possible. The hexa-combo LWD assembly supported optimum well placement and provided valuable information about the geological structure through the analysis of high-resolution electrical images identifying the structural events which cause compartmentalization, confirmed by FTS results. This integrated LWD approach enabled proactive well trajectory adjustments to maintain the wellbore within the optimum porous, permeable and fractured target zone. This integrated methodology improved the contact within the water-injection target of the horizontal section, in a challenging thin reservoir and achieved 97.5 % exposure. Using an integrated LWD hexa-combo BHA and full real-time analysis the objective was achieved in one run with zero Non-Productive Time (NPT) and without any real-time or memory data quality issues.

2D Electrical Resistivity Imaging of Bedrock Fissures in Ogbomoso, Southwestern Nigeria

2D electrical resistivity surveys were conducted around the site of the failed proposed Ogbomoso North Secretariat building with a view to examining the trend of suspected bedrock fissures and assessing the vulnerability of structures in the vicinity to potential failure. Electrical Resistivity Tomography data were acquired along ten traverses 80-200 m long each, using the dipole-dipole electrode configuration with station interval of 5 m and expansion factor, n, varied from 1 to 6. The data were processed by using 2D resistivity inversion technique in the DipproTM software package to generate 2D resistivity sections beneath the traverses. The 2D resistivity sections delineated 2-19 m thick typically clay overburden underlain by bedrock with resistivity ranging from 103 to 59767 Ωm, and anomalously low resistivity zones suspected to be fissures within the bedrock. The bedrock fissures are generally 5-20 m wide and occur at depths ranging from 5 m to ˃25 m beneath the traverses. The fissures trend southward toward the roundabout and front of the College of Health Sciences premises. The incessant road failures and groundwater seepages observed within the study area are attributable to the network of bedrock fissure.

Geosteering Optimization Using the Multi-Boundary Detection Technology in Rubiales' Field, Colombia

Horizontal drilling is part of the development plan for Rubiales field in Colombia, operated by the National Oil Company. By this, different geosteering technologies have been applied during the infill drilling campaign and, it has varied over time. The multi-boundary detection tool has successful results in terms of net sand percent increase, precise location, and cost decrease, related to drilling operations. Some of the challenges for well placement are thin thickness channels with no lateral continuity (deposition environment), oil-water contact closeness, poor correlation with cutting samples, between others. The technology minimizes risks with the real-time resistivity inversion. This process generates a visual representation of the resistivity profile around the wellbore, including geometric definition, dip, and thickness estimation. These inversion results are used to recommend trajectory adjustments while drilling. The complete geosteering experience in Rubiales with the new technology (more than one hundred sixty producing wells so far) has been classified into three main types of wells: lateral sections drilled in continuous sand intervals; lateral variation of resistivity; and wells with a change of prospective zone by channel discontinuity. The implementation success is described by the net sand percentage increasing, around 16% compared with other technologies. The average drilling length was improved by 20% and the number of geological sidetracks concerning previous stages of exploitation reduced by more than 90%, without affecting the drilling rate. These factors, including the update of the sedimentological models, inclusion of new reserves, and the production increase, are part of the optimization plan.

Porosity Prediction from Gravity Inversion with Constraints from Resistivity Data

This work describes a method to carry out 2-D inversion of gravity data in terms of porosity and matrix density distribution using previous DC resistivity inversion results to constraint the fractional pore-water content in the rocks. The inversion is carried out using a controlled random search (CRS) algorithm for global optimization. The method was tested on synthetic data generated from a model representing a graben, and the results show that it can estimate accurate values of contrast-density and porosity. The method was also applied to gravity and dc experimental data collected in NE Portugal, showing results that agree quite well with the known geological information.

3D spatial characterization of sand body for uranium reservoir based on geostatistical resistivity inversion

The current energetic transition policies reenabled the importance of producing nuclear energy in producing electricity. Uranium is the principal fuel used in nuclear power plants, and mineral deposits containing this element are of strategic importance. The successful development of sandstone uranium deposits benefits from three-dimensional (3D) geophysical characterization of sand bodies in uranium reservoir. To solve this problem, a method based on 3D geostatistical resistivity inversion is adopted. Firstly, we analyze the application of that method to the problem in hand and introduce a workflow for analyzing the data. Secondly, through petro-physical sensitivity analysis, we identify the logging parameters that can characterize sandstone in this context, and we use that as the parameter estimated by the geostatistical inversion outlined herein. Then, the 3D data of inversion representing the sandstone of uranium reservoir is obtained by the 3D geostatistical resistivity inversion, demonstrating an accuracy well within an acceptable level of accuracy. Finally, the 3D data of inversion is applied to 3D spatial characterization of a sand body in uranium reservoir inverting a field dataset. Our method is useful in determining the location of drilling wells for exploration and development of sandstone uranium deposits.