| Abstract |
Correlation of borehole geology with results of acid-stimulation of 10 wells in the Greater Tongonan geothermal field was conducted to determine if the wells S responses to acidizing are related to specific geological parameters. The acidized wells were selected based on confirmed mud damage (I09D, II OD, MG-7RD), reduced well capacity due to silica deposition (2R4D, 5R7D), and inherent poor permeability (4R6D. IRIO, MN-I, MG-8D, MG-IOD). The results of the acid-stimulation indicated that the mud damaged wells generally showed the largest improvement as measured by the absolute increase in injectivity index before and after acidizing; the wells clogged by silica deposits showed moderate improvement while the inherently tight wells displayed minimal improvement. The improvement in the wells could not be positively correlated to specific operational parameters such as the volume of acid used, the aggregate thickness of the acidized zones, and the pump pressure employed. Our correlation also showed that such geological features as the temperature, dominant alteration type, and even abundance of calcite veins in the acidized pay zone do not exert any significant role in determining improvement in well permeability during acid-stimulation. The geological parameter that has a direct influence on the acidizing results is the lithologv of the acidized payzone. Wells whose payzones occur within the Mahanagdong Claystone invariably displayed little or no improvement confirming the inherent tightness of this formation. Those wells whose acidized zones occur within the Mamban Formation and Mahiao Sedimentary Complex displayed variable improvements but are generally more improved compared with those wells within the Mahanagdong Claystone. Another factor that appears to pre-determine success in acid-stimulation is the presence of total circulation losses in the payzone. Wells whose acidized zones have associated total drilling circulation losses displayed better improvement as a group compared with those without associated total losses of circulation in the acidized zones. Only well 109D displayed results that are somewhat inconsistent with the general trend. Because inherently tight wells respond poorly to acidizing, it is recommended that future acidizing jobs be concentrated on mud-damaged and mineral-clogged wells. The target payzones of these wells should be hosted by either the Maniban Formation or by the Mahiao Sedimentary Complex and must have associated total drilling circulation losses. Lastly, because our study is site-specific, its applicability to other geothermal fields needs to be independently validated. |