Miscellaneous Subsurface Methods 755 



the Lansing limestone (Pennsylvanian) is treated just after the first short 

 production test with 2,000 to 5,000 gallons of acid under pressure. The 

 initial production is increased up to 320 percent. The limestone is coarsely 

 crystalline, fossiliferous, and oolitic and contains streaks of chert and shale. 



(3) Production from the Viola limestone of the Greenwich field of 

 Sedgwick County, Kansas,^^ is substantially increased by adding 1,000 gal- 

 lons of acid before potential tests and toward the end of the well's economic 

 limit (fig. 403). 



(4) In the Hugoton gas field in southwestern Kansas,^^ the dolo- 

 mitic-limestones of the Big Blue series (Permian) are generally treated 

 with 8,000 gallons of acid applied in two or three stages. Most wells in- 

 crease in open-flow capacity of about 200 percent. Nine hundred percent 

 increase has been the maximum. 



(5) In the Wasson field, Yoakum and Gaines Counties, Texas,^* the 

 common acid treatmeiit consists of three stages involving a total of 8,700 

 gallons. The acidization is carried out in the San Andreas porous dolomite 

 of Permian age. Six to fourteen days are required for the treatment. The 

 chemical used includes inhibitors, demulsifiers, activators, and other phys- 

 ical and chemical modifiers to improve the treatment process. 



Methods of Locating Porous Zones 



(1) Diamond Coring: Because of high core recovery by diamond 

 coring, porous and fractured intervals in carbonate rocks may be more 

 clearly delimited. 



(2) Well Cuttings: Examination of carefully controlled well cuttings 

 frequently afford a means of locating permeable intervals. The details of 

 the permeable intervals, however, cannot be accurately evaluated by this 

 method. 



(3) Lost Circulation: Interruptions in the mud circulating system 

 serve as an index to the position of permeable zones. Lost circulation, how- 

 ever, does not indicate a petroliferous interval ; water may be the prevalent 

 fluid. 



(4) Thermal Data: Theimal-log surveys have frequently indicated 

 hot and cool points in the mud column, a fact which suggests flow of 

 either fluid or gas or both. 



(5) Electric Pilot Survey: This method involves covering the ex- 

 posed well section to be evaluated with an electrical conducting medium 

 (salt water) . The fluid is then forced into the formation at a uniform rate 

 by an oil column. The rate of depression of the oil-water interface is then 

 recorded with a current-contact electrode. These data are recorded and the 

 permeable intervals determined. 



*^ Bunte, A. S., Subsurface Study of Greenwich Pool, Sedgwick County, Kansas: Am. Assoc. Petro- 

 leum Geologists Bull., vol. 23, no. 5, p. 657, 1939. 



*^ Barth, G. G., and Smith, R> M., Relative Porosity and Permeability of Producing Formations of 

 Hugoton Field as Indicated by Gas Withdrawals and Pressure Decline: Am. Assoc. Petroleum Geologists 

 Bull., vol. 24, no. 10, p. 1803, 1940. 



** Schneider, W. T., Geology of the Wasson Field, Yoakum and Gaines Counties, Texas: Am. Assoc. 

 Petroleum Geologists Bull., vol. 27, no. 4, p. 521, 1943. 



