How Halliburton set a Latin American TCP record

Overview 

In deepwater environments, well testing is a very expensive process coupled with its associated safety aspects. Properly characterizing a well has a significant impact on asset management. Wells are routinely stimulated to remove formation damage, but subsequent testing to determine the skin after stimulation is seldom carried out due to the expense and safety factors. In deepwater Gulf of Mexico, an operator routinely injected xylene into their wells to remove formation damage associated with asphaltene, but they did not have a method of monitoring the effectiveness of the stimulation treatment apart from flow rates observed at the wellhead, which can be misleading.

Challenge 

The operator’s challenges were two fold. Since they had been observing different salinity water on the separator relative to the formation water salinity, they were of the opinion that there may be an aquifer further below the producing sand contributing to the observed water on the surface via either a casing leak or from coning through the bottom perforations. As with other wells in the Gulf of Mexico, asphaltene deposition poses a limit on the allowable drawdown. The well had been routinely injected with xylene throughout its history for asphaltene mitigation. The flowing bottomhole pressure is considered to be near or below the asphaltene onset pressure (AOP). Characterizing the effectiveness of the treatment and whether the treatment needs to be changed was a key challenge for the operator. If the treatment was ineffective, it had to be identified in real time so a remedial action could be taken.

Solution

Halliburton recommended running Multi-Rate Multi-Zone (MRMZ) production logging across the targeted pay intervals. For the MRMZ process, the well flows at three different flow rates followed by a shut-in period. During these different rates, traditional production logging measurements were carried out at each choke setting followed by a stationary measurement at a predetermined depth for 15 min. Once the well was shut in, the tool was parked between the two pay zones, and a buildup was carried out until radial flow was fully established. The traditional production logging passes would assist in determination of the entry point(s) of water, along with hinting at the possibility of its source, while the buildup would help evaluate the skin of the well after the initial stimulation treatment.

Result 

Though the production had doubled after the initial stimulation treatment with xylene, the high skin observed in real time from the MRMZ pressure transient analysis prompted the operator to change the formation damage removal program and to stimulate with hydrochloride (HCl) rather than only xylene. This resulted in an immediate four-fold improvement of productivity index with a potential of further doubling. The highlight of the job was the real-time identification of high skin with MRMZ test, allowing the operator to rethink the stimulation strategy with a relatively low-cost procedure. This change to the operator’s program saved USD 2 million.