SUCCESSFUL IDENTIFICATION OF THIN CARBONATE ON PALEO-BASEMENT HIGH: SPECIAL CASE IN PALEMBANG HIGH, SOUTH SUMATRA BASIN

摘要

Oil and gas exploration in the carbonate reservoir in South Sumatra Basin has been carried out intensively during the last 20 years, especially after the Kaji-Semoga Giant Oil Field discovery in 1996. In this area, the carbonate rock overlying the paleo-basement high is generally thin and difficult to identify from conventional seismic data. Most of the carbonates in the Palembang High were developed in carbonate platform depositional settings with a minor possibility of patch reef build-ups. It is almost impossible to interpret the presence of the carbonate in 2-D and 3-D seismic without integrating special geophysical efforts with a regional geological model. There is a large variation in the internal rock heterogeneity of the carbonate rocks, which causes a wide range of rock properties, including that of porosity and permeability. The lateral rock facies changes have increased the degree of uncertainty for exploration. Although these changes could be on a small scale, just within a few meters, they could result in unsuccessful exploration drilling. Another difficulty is that there exists the possibility of absence of carbonate reservoir on top of paleo-basement high. Observation of the seismic character of the basement and carbonate rocks on paleo-basement high is crucial. Carbonate rock has its own specific character, for example, thickening of reflector or decrease in frequency. Another aspect affecting the seismic character is the rock immediately above the carbonate. Density and velocity contrast between both types of rocks have caused significant reflectivity contrast. The carbonate rocks in the Palembang High have much higher velocity compared to the overlying Telisa shale. Seismic gather and attribute analyses are useful in that they lower the reservoir risk component. Gather analysis will increase the ability to ascertain the presence of carbonate and tuning effect, and high frequency enhancement applied to seismic data provides the opportunity to generate better seismic interpretation. Instantaneous frequency is the most suitable method for determining the tuning effect of seismic data. However, all of these methods are limited in their application. The objective of this paper is to share our knowledge on cost-effective exploration methods and on how we can successfully determine thin carbonate reservoir on paleo-basement high, Palembang High, South Sumatra Basin.