地層温度の推定 検層時坑底温度の補正法とその問題点

Abstract

A theoretical Homer-type analysis of temperature which have been proposed by DOWDLE and COBB (1975) is recently used to obtain static formation temperature (TFbuild) from bottom-hole temperature (BHT) recorded during logging operations.Reservoir temperature recorded in conjunction with bottom-hole pressure surveys (TBHP), temperature recorded during drill stem test (TDST) and TFbuild, which are regarded as true formation temperature (TF), are related to the BHT associated with the first log run. Hence, the following equation is derived: TF=K•BHT+α…Eq. 1 The coefficient K of Eq. 1 varies from 1.04 to 1.71 with the increase of geothermal gradient determined from the TF. For examples: TF=1.54 BHT-9.8 at 5.62-5.75°C/100m TF=1.13 BHT+1.4 at 2.10-2.60°C/100m It has been pointed out that the values in recorded BHT are too low in the high geothermal gradient area. The above regression lines gather at an intersecting point of BHT=25°C and TF=30°C, approximately. When the intersecting point is an origin of new co-ordinates, the Eq. 1 is given by; TF=A•BHT (A_??_K, BHT_??_25°C)…Eq. 2 The coefficient factor A of Eq. 2 is expressed as a function of geothermal gradient (GGBHT) determined from the BHT. A=0.21•GGBHT+0.73…Eq. 3 (1.36_??_GGBHT_??_4.49°C/100m) The estimated formation temperature (TFeq) can be calculated from the BHT by the Eq. 2 and 3. It is necessary to consider that the BHT rapidly rises after mud circulation stopped in the high geothermal gradient area, and changes by the effect of mud circulating time.This empirical method is useful to determine the estimated formation temperature from the BHT, when the Homer-type analysis is not applicable.