• PDF / 836,765 Bytes
• 16 Pages / 439.37 x 666.142 pts Page_size
• 86 Downloads / 249 Views

DOWNLOAD

REPORT

---

Basin Modeling in the Kuqa Depression of the Tarim Basin (Western China): A Fully Temperature-dependent Model of Overpressure History Guangren Shi

Received: 25 September 2006 / Accepted: 17 August 2007 / Published online: 15 December 2007 © International Association for Mathematical Geology 2007

Abstract The fully temperature-dependent model of the effective pressure of the solid matrix and its related overpressure has been derived from the pressure balance equation, mass conservation, and Darcy’s law, and is directly useful in basin modeling. Application of the model in the Kuqa Depression of the Tarim Basin in western China proves that this overpressure model is highly accurate. The case of the presentday values of the calculated overpressure histories of Wells Kela2 and Yinan2 approach the field-measured data with mean absolute relative residuals of 3% and 5%, respectively. This indicates that the overpressure simulation is a practical alternative to using rock mechanics experiments for effective pressure measurement. Since calculation of the overpressure history uses the geohistory model and geothermal history model simulation outcomes, the relevant data used and the output of the two models of the Kela2 well are given as examples. The case studies show that the pore fluid density and viscosity used in the calculation of overpressures should be temperature-dependent, otherwise the calculation results would deviate far from the field-measured pressure data. They also show that the most sensitive parameter governing overpressure is permeability, and permeability can be calculated by using either the Kozeny–Carman formula or the porosity–power function. The Kozeny–Carman formula is better if accurate data for the specific surface area of the solid matrix (Sa ) exists, otherwise, the porosity–power function is used. Furthermore, it is vital for calculating an accurate overpressure history that one can calibrate Sa in the Kozeny–Carman formula, or index m in the porosity–power function by using field-measured pressure data as a constraint. In these specific case studies, the outcome found by using the Kozeny–Carman formula approaches the outcome found by using the porosity–power function with m = 4, and both approach the field-measured pressure data. G. Shi () Research Institute of Petroleum Exploration and Development, Beijing 100083, People’s Republic of China e-mail: [email protected]

48

Math Geosci (2008) 40: 47–62

Keywords Effective pressure history · Basin modeling · Parameter sensitivity · Well Kela2 · Well Yinan2 1 Introduction Overpressure develops and varies during the deposition of a basin. It is not only an important geological event, but also one of the major causes of drilling accidents. Hence, the numerical modeling of overpressure history has been a focus of study in recent years. In basin modeling systems, formation overpressure is deduced from the effective pressure of the solid matrix. The effective pressure is a function of porosity, and is found in two ways: by drawing a curve of effect