Characterization of Sampling-While-Drilling Operations

Abstract

The while-drilling environment poses several potential challenges to acquiring representative formation-fluid samples; in particular, sampling times are expected to be restricted (perhaps severely) and dynamic filtration conditions are expected to predominate. With the aim of formulating effective strategies for sampling-while-drilling (SWD) operations, it is natural to seek answers to at least the following questions: When should samples be acquired-immediately after drilling the formation when invasion is shallowest, or after some time when the mudcake is more mature? What is the effect of circulation rate on sample quality? What levels of sample quality are achievable under while-drilling conditions?The first part of the paper describes the SWD tool used to investigate the questions posed. The tool is composed of the following components: a probe module; a pump-out module, which contains within it fluid-property sensors, including a resistivity cell and a 10-channel optical spectrometer; sample-capture modules; and a power-generation module consisting of a dedicated mud turbine and alternator that provide the required pumping power to the sampling tool.The second part of the paper is devoted to the description and analysis of a series of tests performed to characterize SWD operations. In particular, the following aspects were studied for their effect on sampling efficiency and sample contamination: time after drilling, mud-circulation rate, ceasing and resuming pumping operations as a means of mitigating sticking risk during protracted pumping operations, and the integrity of samples captured under drilling conditions. All tests were performed in water-bearing formations drilled with a water-based mud. A wireline sampling (WLS) tool was run after the while-drilling tests were completed in order to compare the performance of the two sampling tools.The principal conclusions derived from the tests conducted are that present-day sampling technology can be made to survive and operate effectively under drilling conditions, and that there appear to be substantial advantages to acquiring samples soon after drilling a formation. SWD-Tool DescriptionThe SWD tool as currently configured consists of the following modules: a probe module, a pump-out module, sample-capture modules, and a power-generation module (see Fig. 1). The probe module is a modified version of a formation-pressure-while-drilling tool . Modifications to the formation-pressure-while-drilling tool include a larger-diameter probe (0.82 in. in diameter compared with 0.56 in. for the pressure-while-drilling tool), a larger surface area of the sealing packer, a sampling flowline extending from the probe to the bottom of the tool, and a pair of valves whose purpose is to isolate the pressure-measurement section from the rest of the tool during sampling. In normal operation, the isolation valves are positioned to allow the probe to communicate with the pressure-measurement flowline. The pump-out module contains an electromechanical direct-drive pump, pressure ...

Analysis and application of prediction model for formation fluid sampling time while drilling

“…It is very important to obtain geological parameters such as fluid type and property by collecting representative formation fluid samples, which is of great significance to accurately determine the oil-gas situation of reservoir and reasonably formulate medium and long-term development plan of oil and gas field [1][2] . At present, there are two main ways to obtain formation fluid: wireline formation sampling and formation sampling while drilling (FSWD) .…”