Alkali Solution Erodes Shale: Influencing Factors and Structural Damage Characteristics
Table 1
Downhole problems during drilling shale wells in Sichuan Basin and Ordos Basin.
Wells
Basins
Formations
pH of drilling fluids
Downhole problems
W-H1
Sichuan
Longmaxi
11.0∼11.5
Borehole collapse occurred and a large amount of black collapsed debris with a size of 5∼8 cm returned from the well head when drilling shale formations (1856∼2611 m)
W-H3
Sichuan
Qiongzhusi
11.0∼11.5
Serious shale collapse caused pipe sticking at 3642.24 m so drilling finished in advance
N-H1
Sichuan
Longmaxi
11.0∼11.5
Shale sloughing often occurred, and a large amount of black collapsed shale debris returned from the well head during drilling; pipe stuck happened when picking out drilling tools
Y1
Sichuan
Longmaxi
11.0∼11.5
Serious lost circulation and shale collapse occurred when drilling a horizontal zone
Z101
Sichuan
Niutitang
11.0∼12.0
Serious wellbore diameter enlargement
DP1
Ordos
Yanchang
11.0∼12.0
Serious lost circulation (leakage volume was 177 m3) and shale collapse occurred when drilling from 1960 to 2100 m
JH-x2
Ordos
Yanchang
10.0∼11.0
Ratio of wellbore diameter enlargement ranging from 38% to 60%
