Characterization and prevention of formation damage during horizontal drilling

The effect of various factors on the productivity of horizontal wells was q uantitatively analyzed. The results show that formation damage is an import ant factor affecting productivity for the low-permeable sandstone formation s studied. The effect of formation damage for a horizontal well on producti on rate is consistently much higher than that for a vertical well drilled i n the same formation. The design criteria, formulations, properties, and ap plications of three low-damaging drilling muds were discussed. It was obser ved that the three fluids provided excellent formation protection with much lower skin factors and much larger percentages of regained permeability as compared with other commonly used drilling muds. The oil production rates of most horizontal wells are three to five times higher than that of their adjacent vertical wells, which is highly related to the effective preventio n of formation damage.