Sample Fidelity of Formation Sampling While Drillings

Formation sampling while drilling (FSWD) technology has become a research hotspot in oilfield development at home and abroad. The technology is characterized by a comparatively short operation time. Since the operation time is short, the obtained formation data are closer to the real situation in the reservoir. After the formation fluid enters the sample chamber from the sampling module, sealed, and returns from the downhole to the surface, the change in ambient temperature and pressure causes the sample volume to shrink and the sample pressure to decrease correspondingly. The change in temperature and pressure leads to irreversible phenomena such as phase transformation or degassing, which can affect the quality analysis of the sample. To avoid the phenomenon, the pressure in the sample chamber is maintained above the bubble point pressure by pre-charging nitrogen on the ground and boosting adjustment in the downhole, so that the formation sample fluid is consistent with the phase state in the original formation when it is retrieved from the ground. The described method is used to provide results close to the real parameters in the reservoir. As the pre-charged nitrogen and the final sample occupy different cavities of the same vessel, and the volume of the vessel is constant, the change in the parameters, including the sampling volume, temperature difference, and pressure difference between the ground and the well bottom, will cause a change in the pressure of the pre-charged nitrogen. Therefore, the problem of ensuring sample fidelity has become the key to sampling technology. To solve the problem, the method of combining ground pre-charged nitrogen pressure with downhole sample chamber pressurization has been introduced.