Oil giant overcame salt structure and saved $10 million

Overview 

On a new well, in the last section before the reservoir, this operator hit an unexpected salt layer it couldn’t see with conventional surface seismic. After drilling through 30 meters of salt, with no end in sight, the company considered abandoning the well, but wanted a technique to image below total depth before doing so. Halliburton urged the operator to consider an innovative look-ahead VSP technique – a first for this area. Look-ahead VSP would allow the operator to image the base of salt to determine its depth. Halliburton processed the data overnight and determined that the company was only 150 meters away from exiting the salt and hitting the reservoir. With that information and renewed confidence, the operator decided to continue drilling – and found the base of salt just one meter away from Halliburton’s prediction. The operator also used Halliburton’s borehole seismic data to plan the next well locations. The success of the project led the company to award Halliburton five additional wells.

Challenge 

The operator had drilled a well more than 5,500 meters in a carbonate section, when they struck unexpected salt. Due to poor resolution and lack of reflectivity between carbonates and salt – which obscured the salt’s boundaries – they couldn’t determine the base of salt from the original surface seismic survey. Drilling through salt is expensive and risky so the company had to decide whether to continue drilling or abandon the well.

Solution

Before abandoning the well, Halliburton recommended an innovative zerooffset VSP survey to estimate depth-to-drill ahead of the bit, which was a first for the area. The look-ahead VSP survey provides accurate time/depth information and a true seismic image at the wellbore. This technique enabled the operator to “look” hundreds of meters ahead of the bit and discover the depth of the salt structure and top of the reservoir. With this knowledge, they could make an informed decision. 

Because of the stand-by rates for an expensive rig, Halliburton had to provide its depth prediction as soon as possible. Halliburton mobilized the necessary equipment to the rigsite and acquired the borehole seismic data in just 18 hours. Then, Halliburton delivered the data to the nearest processing center more than 40 kilometers away. There, analysts worked overnight to process the data and provide a recommendation to the operator in the morning.

Salt tends to move during drilling and pore pressures directly beneath salt can be unpredictable, creating a risky environment. The data acquired from the look-ahead VSP survey helped the operator minimize these risks while drilling through the salt. Halliburton also used information obtained from the VSP to help estimate the subsalt pore pressure. The company updated the well plan, drilling parameters and drilling fluids accordingly.

Result  

The operator safely exited the salt formation and tapped into the reservoir in 149 meters – just one meter away from Halliburton’s prediction. The accurate interpretation helped the operator save the well. The company saved its investment of close to $10 million in well costs by spending $100,000 on a lastminute VSP.