Abstract
Ying-Qiong Basin is a typical high-temperature and overpressure basin, which is the main battlefield of oil and gas exploration in South China Sea and has made great breakthroughs in recent years. During drilling process in high pressure, the relationship between the deep and the pressure is directly related to the drilling safety and costs. In order to improve prediction accuracy, the VSP operation is carried out through the midway, and three points have been obtained: 1) The VSP has a higher accuracy of the interface depth in certain depth range of the drill bit. 2) When the low-frequency trend prediction is accurate before the drill bit, interval velocity of the VSP inversion is consistent with the formation velocity. 3) The VSP pressure forecast is based on the inversion layer velocity and under-compaction pressure. If the velocity prediction is not accurate, the pressure forecast must be erroneous. If the pressure has other sources, the formation pressure is not accurate even if the inversion velocity is accurate. The application scope and exploration effect of midway VSP operation are summarized and applied to Ledong 10-1 block in Yinggehai basin, which realize the breakthrough in the field of high temperature overpressure and provide the basis for other similar exploration areas to do VSP operation.
Highlights
The application scope and exploration effect of midway VSP operation are summarized and applied to Ledong 10-1 block in Yinggehai basin, which realize the breakthrough in the field of high temperature overpressure and provide the basis for other similar exploration areas to do VSP operation
Abnormal high pressure is mainly due to the late rapid subsidence and under-compaction mudstone formed by rapid deposition, which relies on steady subsidence and weak tectonic activity to maintain [1] [2] [3] [4]
Because of low drilling density and high drilling cost, prediction accuracy of pre-drilling time-depth relationship as well as formation pressure structure is not very high, so it is necessary to update in time by use of drilling data during drilling process
Summary
Because of low drilling density and high drilling cost, prediction accuracy of pre-drilling time-depth relationship as well as formation pressure structure is not very high, so it is necessary to update in time by use of drilling data during drilling process. Midway VSP is a more practical targeted technology in high temperature and high pressure field of South China Sea, which is frequently used and can be measured with high precision and without delaying drilling cycle during the intermittent drilling interval. According to the midway VSP measurement and prediction, the deep relationship and wellbore structure will be adjusted to improve drilling safety and save drilling costs. Application scope and exploration effect of the midway VSP operation in high temperature and high pressure field in recent years are summarized in this paper, which can provide evidence for other similar exploration areas
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