DEVELOPMENT OF WELLBORE TREATMENT TECHNOLOGY FOR IMPROVING PRODUCTION EFFICIENCY FROM AUSTRALIAN OIL AND GAS WELLS

Abstract

Low permeability or formation damage during drilling and completion procedures is often a serious threat to the economic development of a series of Australian oil and gas reserves. In this paper the Pacoota Sandstone in the Amadeus Basin has been considered and the effects of clay mineral morphology, water shock, type and concentration of different salts and varying flow velocity on fines migration were studied. Possible formation damage due to completion fluids and remedial measures such as matrix acidizing were also evaluated.

The Pacoota Sandstone has been found to be sensitive to the salt concentration of permeating fluids. If the concentration falls below a threshold value, permeability begins to decrease drastically. Permeability impairment may further be aggravated if the flow rate of the permeating fluid reaches beyond a critical value. It has also been observed that the typical completion fluid reduces the permeability of the near wellbore region to almost half the original permeability. Use of CMHEC base chalk mud, however, reduces the water loss and consequently the permeability impairment by forming an internal filter cake with a typical honeycomb structure. Mud acid with less than 2.5 per cent HF acid concentration has been found to be insufficient to enhance porosity and permeability of the studied sandstone, rather it reduces the permeability by creating formation fines. Afterflush with EGMBE (10 per cent by volume) and HCl acid also helps to clean-up the small fines created during acidizing. The overall increase in porosity and permeability occurs mainly due to formation of large pore channels by matrix dissolution.