Gas2Grid Limited disclosed Friday that initial remediation procedures have been implemented to free the blocked perforations within the Malolos-1 wellbore in Malolos oil field in Service Contract 44 in Cebu in the Philippines. Those perforations through which the oil is flowed were plugged by clay fines which are being produced with the oil. A weak acid solution was pumped into the formation through the perforations to remove the clay and increase the fluid influx rate.
Significant improvement in fluid influx has been observed although the flow has not yet stabilized. An 8 barrel fluid influx in a 1 hour period was recorded yesterday, with the fluid level in the tubing only having been drawn down to 2,100 feet (643 meters) with the perforations below 7,100 feet – there is still significant back-pressure exerted on the formation. Oil has also been recovered.
Production testing operations will continue with the aim of stabilizing the rate of oil influx while at the same time assessing additional remediation procedures that may be necessary for a continuous production flow.
The swabbing of fluid from the production tubing (tubing volume is 41 barrels) lowers the fluid level and therefore reduces the back-pressure on the oil bearing formations. Recent swabbing, prior to the perforations being blocked, has resulted in the percentage of oil being recovered increasing to almost 100 percent. This result has confirmed that the Malolos-1 sandstones being tested are oil reservoirs.
During the swabbing operations small amounts of fine grained clay have been produced with the oil and this clay has plugged the perforations through which the oil is produced, from the reservoir sandstone into the wellbore. This situation is a common condition with some sandstone reservoirs and it is technically termed “migration of fines”.
“Fines migration refers to the motion of naturally existing particulates in the pore system caused by high fluid shear rates. Generally this is more of a problem in clastic formations (sandstone), due to the higher concentration of potentially transportable materials (such as clay). Fines migration is usually only apparent when the wetting phase (in our case oil) of the reservoir (which wets and encapsulates the fines) is in motion.
Reservoirs displaying severe fines migration problems may be treated by either, reducing production rates (not often a popular choice), increasing flow area by high density perforating, open hole completions, horizontal wells or fracturing to reduce interstitial velocities or chemical stabilisers to adhere the mobile clays to the pore surfaces to reduce the propensity for mobilization.”
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