Xaminer™ Coring Tool

Overview

While drilling an exploratory well in Brazil’s presalt Santos Basin, Petrobras asked Halliburton to perform a complete openhole logging job. The logging program consisted of a full suite of services, including coring. The client wanted approximately 172 core samples. Halliburton promised that it could retrieve at least 30 samples per run. Normally, collecting this many samples would have taken six runs. However, in this case, Halliburton was able to recover 71 large-diameter (1.5 in.) samples on just one of the runs, more than double the anticipated rate. Prejob planning, numerous tool improvements, including the shape of the bit, tool configuration, and real-time monitoring account for the dramatic increase in the success rate, which set a new world record. The dramatic recovery rate saved two deepwater runs that, in turn, saved at least a day of deepwater-drillship time. Between costs for the ship and the crew, the time saved is estimated to be worth more than $1 million.

Challenge

In recent years, Halliburton has made dramatic improvements to its sidewall coring tools. The Halliburton Xaminer™ Coring Tool can withstand temperatures up to 400°F (204°C) and pressures up to 25,000 psi. The third-generation Xaminer Coring Tool can retrieve core samples that are 1.5 in. in diameter and 2.4 in. in length, making them more than three times the volume of the smaller 1-in. samples collected by first-generation tools. Tool reliability and recovery rates have also improved. All of these capabilities would be tested by Petrobras while drilling an exploratory deepwater well offshore Brazil in the Santos Basin. The project was in 2000 m of water, and the well itself was another 4300 m beneath the seabed.

Solution

Because it had little familiarity with this particular field, Halliburton offered the customer the ability to run the Xaminer Coring Tool with a 1.5-in. bit, but also volunteered to have onboard a second Xaminer Coring Tool prepared with a 1-in. bit in case of poor recovery with the first tool. The latter is better suited for very hard formations. Before beginning the job, Halliburton’s research indicated a high likelihood of encountering such rock. To preserve the bit, Halliburton recommended avoiding hard formations in the first runs, but the customer declined to follow that recommendation.

Result

On the first run into the hard formations, 24 samples were collected before bit wear prevented the tool from continuing. On the second run, only 20 samples were retrieved before the same problem developed. For the third run, the customer agreed to follow Halliburton’s recommendation and focus on softer formations. The result: 71 samples were retrieved in a single run, a world record. Of these, 69 were full size and accepted by the customer, making the recovery rate 97 percent. For the fourth run – to collect the remaining samples from the hard formation – Halliburton recommended using the tool configured for 1-in. samples – the best choice for that type of rock.