Published: 03/01/2011
Published: 03/01/2011
Oil-producing wells in some parts of the Middle East often encounter water production, which presents a significant challenge when attempting to stimulate mature reservoirs. Post-acidizing of wells with high water cut could lead to dead wells, or higher water cut, which has an extreme effect on production.
Standard CT stimulations are usually done with no control on acid and diverter placement. Acid volumes are fixed in the designed pumping schedule, regardless of their efficiency, and the stimulation fluids are injected without getting any confirmation that the production zones are treated. The existing water zone often cannot be determined, especially when the information is taken from a production logging tool (PLT) run that was done years ago.
A complete lack of downhole monitoring and control often caused multiple stimulations of oil wells to end up with high water cut.
An operator encountered this problem on a vertical well with four sets of perforations. The well was completed as a perforated cased hole with four sets of perforations and with 4½-in x 3½-in tubing
The latest production logging tool (PLT) run showed water production from the bottom perforated zones, so temporary isolation was required to stimulate the top oil intervals. The well was producing 1,400 bbl/d oil and 55% water cut before the stimulation. The operator was facing the challenge of needing a selective stimulation and called on Schlumberger.
The operator decided to use ACTive Matrix integrated CT production service to optimize CT stimulation through live monitoring of injection rates and downhole pressure and temperature to allow maximum fluid penetration and diversion to optimize treatment volumes. These services enable accurate location and placement of downhole tools to control stimulation.
The stimulation program was enhanced by using real-time distributed temperature surveys (DTS). ACTive stimulation with DTS assists with the real-time control and evaluation of CT matrix stimulation treatments. DTS helps detect the thief zones, determine in real time the diverter efficiency, monitor the stimulation fluids placement, adjust the pumping schedule, and assess the flow contribution during flowback.
The objective of this operation was to acid stimulate the upper zones to remove suspected formation damage and improve well productivity, after isolating the lower zones (water-producing intervals) with a temporary gel plug.
The PROTECTOZONE gel plug was selected to cover the lower zones, and it was successfully placed with CT at the designed depth.
With the help of the ACTive CCL depth correlation, the bottom water zone was successfully temporarily isolated to allow the stimulation treatment to be injected in the uppermost zone.
About four hours of wait time was needed for the plug to gel up and isolate the water-producing intervals before pumping stimulation fluids. DTS was recorded while injecting treated water to confirm the efficiency of the chemical isolation.
To stimulate the oil zones, 20% hydrochloric acid (HCl) with required additives (corrosion inhibitor, iron control, and surfactant) was pumped with pre-flush and post-flush containing mutual solvent while reciprocating the CT across the target intervals.
Post-stimulation, well production showed 43% incremental oil production with no increase of water cut. This confirms that the oil-bearing zones were successfully stimulated with sufficient isolation of the water zone.
The operator has the confidence to use this new stimulation technique to acidize their wet wells without risking higher water cut.
Challenge: Effectively stimulate wells with high water cut using coiled tubing (CT), and eliminate the risk of acidizing high water cut interval during CT matrix stimulation.
Solution: Use ACTive Matrix CT real-time stimulation and conformance service to optimize CT stimulation through live monitoring of injection rates, diverter efficiency, and downhole pressure and temperature to allow maximum fluid penetration and diversion to optimize treatment volumes.
Results: Successfully isolated the water wet zone and stimulated the oil-producing zone. Increased production by 43% without increasing water production.
