Beijing’s longstanding relationship with Khartoum has been a sore spot with international watch groups who accuse China of propping up the regime of Omar al-Bashir in exchange for Sudanese oil. China has vetoed several UNSC resolutions in the past dealing with Sudanese issues, issues that have caused the ICC to issue a warrant for al-Bashir.
Now that the South has seceded and has its own share of the Sudanese oil fields, China is stuck in a difficult position with the recent hostilities between Juba and Khartoum. By not supporting the removal of the autocratic regime of Sudan, the very oil fields that China was hoping to protect for its own usage is now under attack from both sides. Sudan and South Sudan see the oil fields as the economic lifeline of their respective countries, and factions have occupied those of the other country (Sudanese forces to the S. Sudanese state of Unity, S. Sudanese forces to the Heglig oil fields).
Now this conflict threatens to interrupt the flow of oil to China, and South Sudan is looking for Chinese investment on a new oil pipeline so as to avoid having to use the Sudanese one. Had China not been looking at their short term strategic interests, they could have avoided this conflict and interruptions in their Sudanese/South Sudanese oil service.