Reservoir Evaluation Utilizing Integrated Formation Pressure Testing while Drilling Along with Flow Testing Across Burgan Formation
Authors: Al-Dhaferi Yousef , Usman Anes , Al-Fawwaz Abdullah , Al-Khalifah Rehab , Taher Ahmed 
Published: September 2022

Logging-While-Drilling (LWD) formation testers have been successfully used for years in measuring formation pressure and estimating formation mobility. In terms of applications, among many others, this data has been useful for mud weight optimization while drilling, reservoir fluid characterization, and selecting intervals for injectivity tests based on mobility variation. Recently, an LWD formation-pressure-testing-while-drilling (FTWD) tool was deployed in an onshore water-disposal injection well with minimal offset data.

An intensive LWD program was utilized across the Burgan formation, including gamma ray, triple combo, multipole sonic, and FTWD, along with mud-logging and geomechanics services for pore-pressure prediction. Both LWD triple combo and surface logging data were used to confirm lithology for optimum pressure-point selection while drilling, prior to any wellbore damage, evaluating the reservoir for any potential compartmentalization and selection of potential water-injection zones. Due to an unfortunate wellbore collapse, flow testing was not an option to estimate the wellbore injectivity; therefore, the FTWD results were used to select where to drill a sidetrack lateral.

The FTWD direct formation pressure and mobility measurements enriched the understanding of the reservoir by establishing pressure gradients. By interpreting the results of the selected points, reservoir zonation was estimated based on the calculated mobility, which indicated a high degree of permeability variation. Along with consistent formation-pressure measurements, the established water gradient from the measured FTWD pressure-test results while drilling were used as a baseline for comparison with FTWD pressure-test results repeated after a wiper trip. This comparison allowed the evaluation of pressure changes between the two runs and identification of time-lapse effects at the sand face.

The challenging conditions in the drilled wellbore resulted in an unfortunate loss of the main borehole due to hole collapse across some shale intervals. As a result of losing the wellbore, it was not possible to obtain crucial reservoir flow-testing information. The FTWD interpreted data gave crucial insight, facilitating the decision on where to drill a sidetrack lateral that would meet the injectivity requirements. Based on the measured mobility, the sidetrack was drilled and tested for injectivity, yielding favorable results.

This paper focuses on enhancing permeability estimation, along with fluid and mobility identification in clastic formations, utilizing an integrated approach of FTWD and injection testing for better formation evaluation and reservoir characterization. The integration of the LWD data with the water injectivity profile evaluation highlighted the importance of proper characterization of the mobility/permeability of the formation. This in turn provided clue to the observed variation in injection profile with time as shown by periodic PLT logging.