1054 



EXPLORATION GEOPHYSICS 



can be derived from the log in this case regarding the exact boundaries of the beds. It 

 is furthermore impossible to determine the true resistivity of the permeable beds in 

 hard formations, or to determine, even qualitatively, their fluid content. 



Determining Fluid Content. — Efforts have been made for many years to deter- 

 mine the fluid content of reservoirs. In certain areas, a close analysis of the logs, and 

 a careful consideration of all geological data (particularly the results of production 

 tests) often will give an indication of the nature of the fluid content.f Side- wall sam- 

 ples are of help in problems of this nature. 



Fig. 650. — Correlations between 

 two wells in the Tom Ball and 

 Cleveland area along the Conroe 

 trend. (Deussen and Leonardon. 

 Paper presented before A.P.I, at the 

 16th Annual Meeting, Los Angeles.) 



Correlation Between Wells 



Where lateral continuity is prevalent, as 

 is likely to be the case for marine deposits, 

 the sediments are identical in texture, poros- 

 ity, and salinity at the time of deposition. 

 Although these characteristics may have un- 

 dergone important modifications since the 

 deposition, the initial similarity still remains 

 to a large extent because most of the modifi- 

 cations (variation of compactness due to 

 varying pressures, alteration of the ion con- 

 tent of the connate waters, etc.) are of a 

 regional character. For example, the concen- 

 tration of subsurface v^^aters often exhibits a 

 gradual and regular variation ; this makes it 

 possible to identify various horizons by 

 means of isoconcentration curves covering 

 areas of a large extent. | Consequently, if 

 the electrical logs of two neighboring wells 

 are similar or nearly identical, as is often the 

 case, the lithology and conditions of impreg- 

 nation may be assumed to be very similar. 

 On the other hand, decided changes in the 

 form of the diagrams indicate correspond- 

 ing lateral modifications of the geological 

 sections. 



t M. Martin, G. H. Murray and W. T. Gillingham, "Determination of the Potential Productiv- 

 ity of Oil-Bearing Formation by Resistivity^ Measurements," Geophysics, Vol. Ill, p. 258. 



G. E. Archie, "The Electrical Resistivity Log as an Aid in Determining Some Reservoir 

 Characteristics," A.I.M.E. Tech. Pub. 1422. 



M. R. J. Wyllie, "A Quantitative Analysis of the Electrochemical Component of the S.P. 

 Curve," A.I.M.E. Tech. Pub. 2511 (1949). 



M. R. J. Wyllie, "A Statistical Study of the Accuracy of Some Connate Water Resistivity 

 Determinations Made from S.P. Log Data," A.A.P.G. meeting, St. Louis, March, 1949. 



M. P. Tixier, "Electric Log Analysis in the Rocky Mountains," A.P.I, meeting, Los Angeles, 

 1949. 



G. E. Archie, "Electrical Resistivity an Aid in Core Analysis Interpretation," Bull. A.A.P.G., 

 Vol. 31, No. 2, Feb., 1947. 



H. W. Patnode, "Relationship of Drilling Mud Resistivity to Mud Filtrate Resistivity," 

 A.I.M.E. Tech. Pub. 2511 (1949). 



M P. Tixier, "Evaluation of Permeability from a Determination of the Resistivity Gradient 

 on the Electric Log," A.A.P.G. meeting, St. Louis, March, 1949. 



t L. C. Case, W. R. Berger, R. F. Fash, and H. E. Miner, Problems of Petroleum Geology, 

 Part VI, published by A.A.P.G., 1934. 



