No abstract

No abstract

An extensive drilling campaign was done for the purpose of reservoir appraisal of an offshore Brazilian field that included complex deviated pilot wells. One of the objectives of this campaign was to provide detailed reservoir pressure information to determine fundamental reservoir properties. In order to optimize the data collection, it was necessary to acquire pressure measurements and also to transmit real time to validate test responses. Due to the complexity of well trajectories, the solution for executing pressure tests consisted of using Formation Pressure While Drilling technology.The operation was carried out in five pilot wells providing critical results. The first result was the detection of non-linear reservoir depletions. Pressure tests also identified change of fluid phase in a black oil reservoir containing a gas cap. By comparing the fluid phase and gradient from early exploration wells, it was evident that the free gas was not originally present. This multiphase behavior reinforces the second result: confirmation of the dynamic process that reservoir fluids are undergoing. Moreover, different degrees of pressure depletions were observed in locations up to 1.5 km distant from producer well within same connected reservoir proving third outcome: the long lateral connectivity of reservoir sands. Another important outcome is that the actual bubble pressure is higher in magnitude and the current pressure depletion had fallen below it. The final outstanding result was the potential increase of oil reserves where pressure values identified unexpected sand channels with no drainage or very small depletions. The results of this pressure measurements analysis reinforced the need to optimize the potential capacity of oil recovery through acceleration of drilling injection wells for pressure maintenance.

After the progressive advancement of the drilling technologies, such as mud motors and afterward rotary steerable systems, the successful execution of high angle wells became a common practice in the oil industry. Although the associtated costs have much superior magnitude when compared to the ones related to vertical wells, the production factor is normaly improved by multiple times, turning such trajectory design very suitable. However achiving the key performance objectives, e.g., consistent and effective net pay interval along the horizontal section, can be extremely difficult. There are many geological and geophysical reasons, such as the lateral discontinuities of the reservoirs and intrinsic seismic uncertainties. To overcome such challenge, Well Placement technique is used to interactively position the well based on geological and seismic criteria together with real time Logging-While Drilling data. Despite the fact of covering the technical disciplines of drilling, geology, petrophysics and geophysics, most Well Placement approaches rarely take into consideration reservoir engineering aspects when geosteering horizontal wells.Therefore the project objectives were to evaluate the impacts in the productivity generated by the geometrical changes in the trajectory through numerical reservoir simulation. The research work was then divided into two parts. The first one was the creation of a representative 3D synthetic reservoir model where numerical simulations were applied for each trajectory design. A detailed sensitivity analysis was made by comparing the results among the different trajectory cases in order to identify the relationship between well positioning and its productivity response.The second part consisted of a real geosteering case study. Around both planned and executed wellbores, it was created a detailed reservoir model enhanced by LWD inputs. Afterwards, reservoir simulations were performed in order to evaluate the impacts caused by trajectory variations, demonstrating the expected productivity results versus the actual.This research study shows that there is a productivity impact in all reservoir fluids when well trajectory is subjected to geometrical variations. Thus it reinforces that predictions related to reservoir production should not only be performed on planning stage, but most importantly during or after well conclusion using relevant inputs, such as the actual well path, LWD logs, and formation pressures while drilling, which all combined provides an enhanced reservoir model, and so a more accurate forecast analysis.

With the advent of rotary steerable systems, successful drilling of horizontal wells became a reality in the oilfield. Even though the costs are much higher than for a vertical well, the production factor can be enhanced multiple times, making it very attractive. However, the drilling of horizontal wells is extremely difficult, mainly due to lateral lithological discontinuities of the reservoirs and seismic uncertainties. To overcome such challenge, Well Placement technique is used to interactively position the well based on geological and seismic criteria together with LWD measurements. While covering drilling, geology and geophysics, most Well Placement approaches rarely consider reservoir engineering aspects. Therefore the project objectives were to evaluate the impacts in the productivity generated by the geometrical changes in the trajectory through numerical reservoir simulation. The research work was then divided into two parts. The first one was the creation of a representative 3D synthetic reservoir model where numerical simulations were applied for each trajectory design. A detailed sensitivity analysis was made by comparing the results among the different trajectory cases in order to identify the relationship between well positioning and its productivity response. The second part consisted of a real geosteering case study. Around both planned and executed wellbores, it was created a detailed reservoir model enhanced by LWD inputs. To increase prediction accuracy, a refined gridding with variable cell size technique was applied to enhance pressure and saturation sensitivity. The level of precision was improved by using LWD measurements, such as the most precise formation pressure, the permeability near wellbore and the remote boundary mapper technology that provided a detailed reservoir structure based on formation resistivity contrast. Afterwards, reservoir simulations were performed in order to evaluate the impacts caused by the trajectory variations, demonstrating the expected productivity results versus the actual ones. The work delivers a novel ability to construct optimal horizontal wells not only by including conventional Well Placement technique, using geological and geophysical criteria, but also by adding into the workflow an advanced numerical simulation approach. Such integration allows the operator to predict the impacts on the productivity as the trajectory is being changed, and the actual reservoir geometry and its properties are determined by LWD measurements. It also reinforces that predictions related to reservoir productivity should not only be performed on planning stage, but most importantly during or right after well execution using relevant inputs, such as the actual well path, LWD logs, and formation pressure measurements, which all combined provides an enhanced reservoir model, and so a more accurate forecast analysis.