土崎沖油田および雲出ガス田における掘進率と泥水循環の関係

抄録

In the previous paper a method analyzing quantitatively the effect of hydraulics on the rate of penetration has been suggested as a result of laboratory experiments. In this paper an attempt is made at the application of that method to analyze field data. Tsuchizaki-Oki oil field and Kumoide gas field are chosen as typical ones. Results obtained are as follows:
(1) The concept of Bingham's performance line is approximately applied to these fields. It is obvious in Figs. 1 and 4 that a number of penetration rates comes under the performance line and drilling operations are frequently canducted under conditions of unadepuate hydraulics.
(2) The changes of penetration rates under conditions of unadequate hydraulics are estimated with applcation of the equaiton of relative penetration rate which is even a tentative one as deacribed in the previous paper, and they are shown by broken lines in Figs. 1 and 4. At some instance an increase in penetration rate may be possible with increase in bit weight, but at another instance it is necessary for increase in penetration rate to improve on hydraulics rather than to increase in bit weight.
(3) Separation points of penetration rate from performance line serve as a parameter of hydraulic action. The penetration rate at separation point is related with the impact force which is modified for the effect of a bit diameter, and the relationships between them are appraximately linear as shown in Fig. 2 and 5, of which a general form is as follows :
R_b=a+b(D₀/D)²M
where R_b=penetration rate at the separation poin, M=impact force at the bit diameter D, D₀=reference bit diameter, a and b=constants. A quantitative evaluation of the effect of hydraulics may be possible by the use of this relationship. It may be possible, for instance, to estimate an increase in penetration rate attained by replacing a small pump with a large one.
(4) The drillability of a formation may be evaluated with two paraneters, i. e., performance slope and primary intercept. Judging from these two parameters, drillabilities of formations are genarally higher at Kumoide gas field than at Tsuchizaki-Oki oil field.
(5) It is observed at Tsuchizaki oil field that the penetration rate increases in so-called abnormal pressure formation against a tendency to a decrease in penetration rate with the depth.