Application of formation testing while drilling in highly deviated wells with oil-based drilling fluid

Highly deviated well is deployed in the rolling exploration of western South China Sea oilfield to simultaneously probe into multiple layers, and high-density oil-based drilling fluid is used to maintain wellbore stability. Under such circumstances, the conventional wireline formation testing has high operation risks and difficulties, and the conventional sonic, density and resistivity sensors have trouble in accurately distinguishing formation oil and filtrate of oil-based drilling fluids. Therefore, the sampling-while-drilling technique is required to ensure the acquisition of qualified data. The FASTrak Prism, a tool for pressure measurement and sampling while drilling, can run in hole with the BHA and overcome the sticking and blockage issues of wireline well logging. The spectrometry-while-drilling technique enables accurately identifying the formation oil by measuring the (methane) gas content of fluids via the multi-channel density measurement. The field application of the FASTrak Prism-based pressure measurement and sampling while drilling in the reserves assessment for western South China Sea oilfield demonstrates how to rapidly differentiate filtrate of oil-based drilling fluids and formation oil with the help of the spectrometry-while-drilling sensor, and this technique can help to gain key data, such as formation pressure, reservoir physical properties, and fluid properties, for the exploration-development-integrated reserves assessment. The successful application validates the feasibility of the proposed technique in the integrated exploration and development of western South China Sea oilfield.