The Da-4 key high-risk exploration well in Sinopec’s exploration block on the southeastern margin of the Junggar Basin has recently obtained commercial oil and gas flows, with peak daily output reaching 24.12 cubic meters of oil and 6,125 cubic meters of gas, marking the first discovery of a new petroleum system in the area.

The Da-4 well is located in the Chaiwobao Sag of the Junggar Basin and was deployed and implemented by the Exploration and Development Research Institute. The Chaiwobao Sag is an intermontane residual sag formed after bidirectional north–south compressional tectonic modification. The first parameter well, Chai-Can-1, was drilled in 1989 and obtained commercial oil flow. From 1990 to 1999, several exploratory wells were drilled but failed to achieve a breakthrough. After Sinopec took over the block in 2000, wells including Chai-Can-Side-1, Da-1, and Chai-Can-1HF were deployed around the Chai-Can-1 area, but results were unsatisfactory and exploration once fell into stagnation.

Facing this long-standing and highly complex exploration area, researchers adhered to the belief that “where there is a source in the mountains, there must be oil beneath,” and continued intensive scientific research. Through structural modeling, tectonic evolution analysis, and prototype basin restoration studies, they identified favorable directions for near-source exploration in the southeastern Junggar residual sags, selected the Chaiwobao Sag as a breakthrough target, and deployed the Da-4 risk exploration well in 2022.

The drilling process encountered setbacks. When the well reached its designed depth of 5,900 meters, no oil or gas shows were observed in the main target formations. However, through refined oil–source correlation analysis, researchers concluded that the shows originated from deeper source rocks and decisively proposed further deepening of the well.

At a depth of 6,200 meters, good oil and gas shows appeared. The research team promptly conducted comprehensive studies on the cored intervals, accurately determined the stratigraphic attribution, and clarified the hydrocarbon source. Ultimately, source rocks and thick oil and gas layers were encountered in the 6,300–6,550 meter interval.

Zhang Guanlong, Standing Committee Member of the Party Committee and Vice President of the Exploration and Development Research Institute, stated that the breakthrough at the Da-4 well confirms the strong exploration potential of the southeastern margin of the Junggar Basin. The area is expected to become an important successor zone for large-scale reserve additions, injecting strong momentum into achieving new strategic breakthroughs.