Horizontal gas injection well drilled in a sandstone formation with carbonate/polymer mud. Effective mud damage removal was critical to obtaining the required injectivity. After treating the well with an ArcasolveTM acidizing and polymer breaking formulation a linear relationship was demonstrated between the injection rate and injection pressure indicating that the wellbore was clean. Tests achieved a gas injection rate of 15 mmscf/day compared to a predicted a target range of 10-20 mmscf/day assuming no residual mud damage. The operator’s senior completion engineer commented “I do consider this well a great technical success”.
Drilling program was underway using carbonate/polymer mud to drill 6” diameter horizontal open hole wells approximately 2000 ft in length. Existing treatments were only partially effective leaving residual viscous polymer slugs and carbonate solids in mud cake not treated. Wells had to be swabbed for at least 10 days before downhole pumps could be installed and production started. The mud damage clean up treatment was changed to an ArcasolveTM acidizing and polymer breaker formulation and immediately after the treatment produced fluids were clean and free from polymer residues. No swabbing was required, downhole pumps were installed immediately after drilling and production commenced much earlier with spent ArcasolveTM treatment fluid back produced using the downhole pump. Following the initial 3 well trial, ArcasolveTM was used on all remaining wells in the drilling programme for this field, approximately 40 wells in total.
Horizontal well drilled with a carbonate/polymer mud in a poorly consolidated sandstone formation where conventional acidizing could collapse the formation. After drilling the well and circulating liquid mud from the hole with brine the operator pumped an ArcasolveTM acidizing plus polymer breaker formulation. The fluid was placed from the toe to the heel of the well through the drill string and bottom hole assembly as the drill string was pulled out of the hole. After leaving the fluid to soak the well was brought onto production and pressure data from downhole gauges and production data were used to calculate the PI of 223, 10 times the productivity of vertical wells in the same area of the field.
An existing horizontal well was drilled with oil based mud and acidized with HCl through coiled tubing shortly after production was first initiated approximately 9 years before the Arcasolve™ treatment. The total length of open hole in the pay zone is 2306ft and logs run after the HCl treatment indicated that production was from 4 separate zones, between the middle and toe of the open hole, collectively accounting for only 150 ft of the well bore i.e. around 7% of the total open hole. There was minimal pressure drop in the reservoir since the onset of production and only a few percent of the oil in place had been produced. The well was treated by bullheading Arcasolve™ fluid because deploying coiled tubing was not operationally possible. Production increased from around 150 bopd (pre-Arcasolve™) to a peak rate of 800 bopd before levelling off at a stabilised rate of 500 bopd within a few weeks. Six months after the Arcasolve™ treatment production was still well over 300 bopd. The operator proceeded to treat all the similar remaining wells in this field with Arcasolve with similar success.
This field treatment was carried out in an oil production well drilled with water based polymer mud and with a gravel packed completion including a FIV set above the completion. Arcasolve™ fluid was spotted inside the screens in the lower completion through a treatment string as it was withdrawn from the toe to the heel of the well. The lower completion was isolated by the FIV closing as the treatment string was withdrawn and the Arcasolve™ fluid was left to soak before the well was produced. The well came on to production according to the operator’s expectations at an initial rate of several thousand bopd and this mud damage removal technique was subsequently included in a services contract for use offshore by a major state oil company in South America drilling new wells with planned gravel packed completions.
Sand screens were run in a solids free reservoir fluid and gravel packed using a solids free sodium chloride and sodium formate brine containing mononethylene glycol for hydrate suppression. The ArcasolveTM breaker chemicals were incorporated into this gravel pack carrier fluid to ensure immediate close proximity between the breaker fluid and the mud cake. The ArcasolveTM breaker chemicals were carefully formulated to avoid premature mud cake break through during gravel packing.
Production results in the first series of wells were excellent. P/I’s were higher than the operators base case assumptions and the capacity of subsea equipment was the only constraint on production rates.
Similar ArcasolveTM mud damage removal treatments are being carried out on subsequent new wells in this major offshore development project.
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