The Source Rocks Evaluation in Beibu Gulf Basin Using Well Logs

Taotao, Yang
Hangzhou Reserch Institute of Geology, Hangzhou, China.

The Beibuwan Basin, also called the Beibu Gulf Basin, lies in the northwestern corner of the South China Sea. Most of the basin lies offshore with water depths in the range of 0-60 m. The basin originated as a polycyclic rift basin in the Mesozoic. Over the dozens of years exploration, more than 40 oil&gas fields discovered in there, the source rocks have been approved. In the basin scale, mudstones which deposited in semi-deep to deep lacustrine environments of the Eocene Liushagang Formation and Oligocene Weizhou Formation, especially those of the Liushagang 2 and 3 members, are the principal source rocks. As to interest Block, the main aspect of the problem is identifying the source rock and evaluate the produce potentiality of hydrocarbon. Therefore, the source rock identification and evaluation are undoubtedly important for the exploration.

Based on the former studies, it is common knowledge that source rocks show obviously response of well logs data. Owing to our researches, combined with the cuttings data, several logs to source rock show particular features. These are listed as follows, Gamma Ray(GR), including Spectroscopy Gamma Ray(SGR), Thorium(TH), Potassium(PO) and Uranium(UR), Interval Transit Time(DT), Bulk Density(RHOB), Neutron (NPHI). The singular characteristics of each log are elaborated in full in the follow passage. GR, especially the UR, show the readability sharp crest because of attachment radioactivity material. Due to organic material low velocity of mudstone, DT exhibit the low value and flatten tendency. The density of mudstone is more higher than the organic substance, the bulk density of the formation decline. NPHI indicate the hydrogen of formation, so the log representation the crest. Then, the organic contents is estimate using the well logs. Our results agree with the analysis data form cuttings. The method is overcome the disperse and discontinue testing data.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012