‘Triple-Double’ Logs Recorded
No one would question there’s an ongoing high level of activity in Saudi Arabia’s oil patch.
Yet little of what’s happening at national oil company (NOC) Saudi Aramco is transparent -- even though it reportedly manages 260 billion barrels of proven crude oil reserves.
At least one thing is certain: the NOC is into some mighty high-tech new downhole applications.
Indeed, Weatherford International recently announced it successfully ran Saudi Aramco’s first ever EMPulse Logging While Drilling (EM-LWD) triple combo operation (resistivity, neutron, density) with extended range set-up.
It’s all about transmitting the critical downhole information up to the surface -- not a simple task.
In order to send information to the surface while a well is being drilled, some kind of transmission mechanism is required. There are two types of transmission systems available to accomplish this task, according to Tony Branch, eastern hemisphere drilling services technical manager for Weatherford:
- The mud pulse system requires turning on the rig’s pumps to build pressure, and a downhole pulser device sends information uphole through a series of pressure pulses, which are decoded at the surface.
- The other option is to transmit information to the surface via an EM telemetry device, which sends information to the surface via a low frequency electromagnetic wave.
“The EM system has an advantage in the sense there’s time savings,” Branch said. “With the mud pulse system, you have to turn on the mud pumps to send data to surface. With EM it’s automatic and continuous, so you don’t depend on your surface pumps.
“As you’re connecting pipe, you can send information while you’re waiting on the pump pressure to build up.”
It is noteworthy that one of the capabilities of EMPulse-LWD centers on underbalanced drilling conditions (UBD).
“In underbalanced drilling conditions utilizing drillpipe injection, you may not have the fluid column you need to transmit information uphole with mud pulse MWD systems because UBD is basically drilled with a liquid and gas two-phase fluid flow system,” Branch noted. “If the percentage of gas injected with the liquid is too high, then conventional mud pulse MWD systems will struggle to transmit the signal to surface due to excessive signal attenuation.
“In this case you have to transmit through EM -- where you’re independent of what type of fluid is in the borehole.”
The objective of the successful proof-of-concept of EMPulse-LWD with annulus pressure technology at the Saudi Aramco facility was to evaluate the feasibility of EM transmission in conjunction with LWD triple combo and annulus pressure sensors in a 6-1/8 in. horizontal section. The section was drilled underbalanced from 8,109 to 11,189 feet in a single run, according to Weatherford.
The company said drillpipe gas injection on future wells will preclude the use of mud pulse telemetry. Instead, EM telemetry will allow a continuation in the UBD planning process to include real time LWD technology.
Branch noted the evaluation objective at Saudi Aramco was met.
“Real time data allowed 3,080 feet of 6-1/8 in. horizontal section to be successfully geosteered in one bit run while maintaining underbalanced conditions,” he said. “Additionally, the well was flow and pressure tested with real time annulus pressure data acquired during pumps-off operations.
“One advantage of EM versus conventional mud pulse telemetry is that real time updates are possible, independent of wellbore hydraulics.”