Published: 12/02/2015
Published: 12/02/2015
IPTTs in high-permeability reservoirs were not providing sufficient information for an operator in the Norwegian Continental Shelf. Although IPTTs are a proven method for efficiently determining the permeability and permeability anisotropy of formations, they are conventionally conducted with a wireline formation tester. The maximum flow rate at which wireline formation testers can pump formation fluid limits their use to low- and medium-mobility formations, where enough drawdown can be achieved to produce a measurable pressure transient laterally and vertically for tests involving observation probes. An additional constraint is that only a relatively small amount of fluid—tens to hundreds of liters of formation fluid—can be pumped by a wireline formation tester into the wellbore before a wiper trip on wireline is required to maintain well integrity and drilling fluid quality. Furthermore, the radius of investigation is limited to tens of meters, which is usually not sufficient for determining reservoir boundaries and the presence of faults.
To extend testing capabilities, the operator teamed with Schlumberger to develop a new pipe-conveyed wireline formation tester technology that easily manages the high flow rates from high-permeability reservoirs. Flow rates up to 130 cm3/s [0.05 bbl/min] are achieved by FTWT to pump thousands of liters of formation fluid, making it possible to evaluate reservoir properties hundreds of meters away from the wellbore. The hydro-carbons pumped from the formation to the wellbore are reliably circulated to the surface to be appropriately managed while maintaining well control and drilling fluid quality.
FTWT employs a dual packer or quad packer to isolate an interval for testing or it can be paired with the Saturn 3D radial probe. The packers isolate single zones or multiple layers for testing. The wellbore-induced noise that interferes with sensitive pressure measurements is significantly reduced because the annular BOP can be closed during testing.
FTWT was deployed in the Norwegian Continental Shelf to conduct an IPTT in a sandstone with 11-darcy permeability. Total station time was 26 hours, and one of the longest flow periods was nearly 6 hours at a rate of 128 cm3/s. For assumed radial flow, the 6-hour FTWT flow period produced a 576-m radius of investigation, the distance where a 0.01-psi pressure drop could be detected. A conventionally conducted IPTT for 2 hours at 30 cm3/s would have achieved only a 200-m radius of investigation with that sensitivity.
By achieving a longer transient with FTWT, the operator was able to efficiently investigate deeper into the high-permeability reservoir than was possible with a conventional IPTT.
Challenge: Acquire higher quality data and for longer duration while conducting formation transient testing in highly permeable formations than what conventional wireline formation testing tools can achieve and concurrently significantly improve efficiency while reducing testing costs.
Solution: Develop formation testing while tripping (FTWT) technology, which enables conducting interval pressure transient testing (IPTT) at flow rates up to 130 cm3/s [0.05 bbl/min] to extend the evaluation of reservoir properties to hundreds of meters beyond the wellbore while consistently keeping the well in overbalance as all extracted hydrocarbons are circulated out during the test.
Results: Confirmed a radial flow pattern from a 6-hour test that investigated 576 m into an 11-darcy-permeability sandstone where a conventional IPTT would have achieved only a 200-m radius of investigation.
