Loris Tealdi

Using the Continuous NMR Fluid Properties Scan to Optimize Sampling with Wireline Formation Testers

One of the most important objectives of fluid sampling using wireline formation testers (WFT) is to ensure that representative samples of the different fluids encountered in the formation are obtained. Usually the wireline or LWD petrophysical logs will guide the sample acquisition program. This typically means that resistivity and nuclear logs are used to infer basic fluid types, caliper log is used to verify that the borehole is suitable for sampling, and NMR logs are used to gauge if permeability is sufficient for a sample to be taken. However these logs are not able to capture variations in the hydrocarbon column to allow the operator to ensure that all representative fluids are sampled. The most important information, a continuous fluids type and property log, is still not widely used in the industry. Modern NMR logging tools can deliver – in addition to conventional porosity and permeability information – a continuous fluid log of oil, gas, water and OBM filtrate (OBMF) at multiple depths of investigation. The radial fluid profiling allows discrimination of OBMF versus native oil. Additionally, within the hydrocarbon column the NMR measurements can be used to provide continuous logs of oil viscosity and gas-oil ratio (GOR). With this information acquired before the sampling operation, it is easier to ensure that a full suite of representative samples are acquired and that we do not indulge in needless over sampling. When NMR data is acquired after the sampling operation, the continuous logs of viscosity and GOR can be calibrated with WFT data to provide fluid information in places where WFT did not sample.

Fracture Optimization Applying a Novel Traceable Proppant and a Refined Mechanical Earth Model in the Congo Onshore

Fracture stimulation has been adopted as an integral part of the completion in the M’Boundi field given the results achieved in enhancing well productivity, as well as the positive impact realized on field development economics. The fracturing process has been optimized over the years through improved reservoir understanding and ensuing implementation of technologies to address the uncovered challenges. Changes to the fracturing fluid formulation to prevent damaging the water sensitive reservoir rock, as well as modified proppant schedules to mitigate proppant embedment are examples of this improvement process. This paper describes the successful ongoing process of optimizing hydraulic fracturing designs in M’Boundi field. By applying an integrated approach combining various technologies, it was possible to better understand fracture propagation and coverage of the target reservoir. Implementation of a novel non-radioactive traceable proppant allowed accurate frac height measurement at the wellbore. When combined with rocks mechanics derived from sonic logs it led to redefining the mechanical earth model and ultimately the completion and fracturing strategy in the field. The process will be illustrated with examples from a 3-well campaign recently executed onshore Congo.

Hydraulic Fracturing as Development Strategy in the Congo Onshore.

The benefits of Hydraulic Fracturing (HF) are well recognized in the oil industry, even if in many world regions it is still seen as a remedial operation rather than a reservoir development strategy. The big part of worldwide HF operations, are performed extensively in the US and Canada, primarily for reservoir development purposes of tight gas fields. However during the last few years, the global trend has seen a change and HF is now encouraged for adding new reserves, aiding the development of low permeability marginal reservoirs and prolonging life of brown fields. In Congo Onshore, HF is now a consolidated reality, with more than 70 frac jobs pumped. Good results have encouraged management to increase fracturing activity: nowadays HF is performed on all the infill wells that are drilled in the low permeability layers of the reservoir. From the early stages of development only the layers with the higher permeability were produced, while the possibility to develop the low permeability layers was not considered, because of very poor or zero production results due to the application of conventional completion strategy. Since HF is now performed as a standard practice on new wells, it has been reconsidered for the application on old wells completed in the low permeability layers. The challenge encountered on these old wells, has been the presence of long perforated interval. Rigless operations (such as sand plug) and work-over operations (such as cementing of old perforated interval and reperforations) have been needed for fracturing in order to avoid fracture initiation issues like multiple fractures and early screenout.

Hydraulic Fracturing in the Congo Onshore: Continuous Optimization Improves Productivity

This paper describes the successful ongoing process of optimizing hydraulic fracturing designs in a well campaign in Congo onshore to create best practices for continuing development. The fracture design program began by characterizing and evaluating the rock formation and its compatibility with stimulation fluids, including mineralogical and geomechanical properties, as well as regained permeability. For example, laboratory testing determined that the formation was soft and highly sensitive to water, indicating that a water-based fracturing fluid would require specialty additives to minimize formation damage.