Characterize formation porosity and lithology while drilling with azimuthal density measurements (ADN).
Producing since 1971, the Messla Field is one of the largest fields in Libya and North Africa. Arabian Gulf Oil Company (AGOCO) needed to increase production and oil recovery in the vertical HH86-65 well, which was drilled in 2002 and subsequently shut down due to zero oil production.
To increase production, AGOCO decided to sidetrack the nonproducing HH86-65 well to convert it to a horizontal well by successfully placing the well at the top of the reservoir to avoid the oil/water contact (OWC) below. However, this was difficult to achieve due to drilling challenges, poor seismic resolution of the highly faulted area, and relatively high cost of drilling horizonal wells compared with vertical wells.
AGOCO needed a technology to help place the well in a high-quality zone at the top of the reservoir and enable AGOCO to better understand the subsurface geology.
Schlumberger introduced the GeoSphere service, and prejob modeling showed how it could map the top of the reservoir up to 70-ft [21-m] TVD from the borehole. In combination with the Impulse integrated MWD platform and adnVision azimuthal density neutron service, AGOCO used the GeoSphere service in the drain section to map the full reservoir structure and gain a better understanding of the subsurface geology.
The GeoSphere service provided real-time subsurface inversions, identifying subseismic faults and thickening and thinning of the reservoir—with reservoir thicknesses ranging from 20 ft [6.1 m] to more than 70 ft [21 m]. By delineating the full reservoir-scale structure, the GeoSphere service gave AGOCO a better understanding of the subsurface geology, simultaneously identifying the reservoir’s shale cap above and the OWC below.
With the GeoSphere service, AGOCO better controlled placing the trajectory in the sweet spot, avoiding the risk of drilling into the shale above and below. AGOCO gained confidence to drill more footage in the drain after assessing the reservoir, and production increased to 3,000 bbl/d with zero water cut.
“After the success of the GeoSphere service in our wells, I am confident this will change the strategy of our future drilling program and can make the impossible at that time possible after introducing this technology. I am looking forward for the next challenge by using the GeoSphere service in our fields.”
Issa Alaogali, Reservoir Engineering Department Manager AGOCO
Challenge: Convert a nonproducing vertical well to a horizontal well via a sidetrack operation while managing structural uncertainty.
Solution: Deploy the GeoSphere 475 reservoir mapping-while-drilling service to identify subsurface geology and help land well in the sweet spot.
Results: Brought previously nonproducing well to 3,000-bbl/d production without NPT.