GB1412781A - Well logging data processing methods - Google Patents

Abstract

1412781 Data processing systems SCHLUMBERGER INLAND SERVICES Inc 12 Oct 1972 [13 Oct 1971] 47031/72 Heading G4A Well logging measurements are processed by machine to combine the measurements to produce an output parameter, e.g. hydrocarbon density, to adjust the value of at least one of the measurements to a new value and compute a new output parameter, and to compare the original and new values of the output parameter to indicate its reliability. In the process described, logging measurements are used to calculate "derived" measurements of shale content V sh , effective porosity # e , water saturation S xo of mud-invaded zone surrounding the bore and the measured values of γ-ray bulk density # D and neutron porosity # N are corrected for the calculated shale content (48), Fig. 3 (not shown). The corrected values # D and # N are tested (49) to determine whether or not they indicate a hydrocarbon bearing zone. If a hydrocarbon bearing zone is indicated and the resistivity data is consistent with S xo (90), a routine RODET is entered, Fig. 5 (not shown), to compute the hydrocarbon density RHOH, this being followed by a routine ROVAR (Fig. 4, not shown) which modifies the values of # D , # N , V sh , S xo by predetermined amounts, derives corresponding new corrected values for # D , # N and computes a new value RHOH<SP>1</SP> for RHOH. Fianally a reliability factor VAR is calculated proportional to the modulus of RHOHKHOH<SP>1</SP>. If the VAR indicates reliability (53) RHOH is printed out together with the depth level, V sh , # # and VAR, and when three or more consecutive depth levels with reliable values of RHOH have been found, a running average ROM is maintained over the last three levels for use as a minimum value ROMIN in other parts of the program. If step (49) indicates a non- hydrocarbon bearing level RHOH is set to the density for oil and ROVAR is run to test the reliability of the assumption. If the resistivity measurements (90) are inconsistent with the calculations of step (48), V sh is modified by increments until # D ## N (49) or V sh becomes substantially zero in which case the data is considered unreliable, RHOH is set to ROM and a move is made to the next level. An initial pass through the logging data may be made, Fig. 6 (not shown), to identify sand and shale formations and compute reliable values of RHOH from reliable data derived as deep as possible in each formation, a boundary between adjacent intervals having potentially different values of RHOH being declared when a shale formation thick enough to act as a barrier against hydrocarbons is detected. A plurality of reliable values are averaged to from a preselected value of RHOH for use in the process described above.