Noninvasive stimulation opportunities in a marginal gas field.
Dan-Paul Ştefănescu, Alexandru Nitulete
Vol. 33, no. 2 (2016), s. 507-513, [1]
The Laslau Mare field is a brown gas field in the Transylvanian Basin. The field was developed in the 1970s and the production consists of more than 99% methane gas and low WGR (average of 0.03 m3/kscm). Current reservoir pressures are at a less than a third of initial values. As in any mature field with increasing water production and reservoir pressure depletion, several degrees of formation damage and tubular obstructions have been observed. Mud invasion, plugged perforation, water blockage and scale precipitation at the near wellbore region are factors impairing wells to produce at potential. Adding to the above the fact, the reservoir is water sensitive (low reservoir pressures and water wet reservoir). Severe constraints on production were seen when performing any sort of operation requiring the use of water based fluids, as severe losses occur. These procedures have always given post-job challenges to production engineers. Skin induced by mud or liquid losses is highly affecting wells post job performance. Long recovery times have been observed following workovers’ operations in Laslau Mare (0.5 to 2.5 years recovery for workovers and one to three months for wash treatments). Perforation and re-perforation operations are one of the best way to overcome the formation damage, bypass the invaded zones and open new production zones. Historically, perforation was done with casing guns in overbalanced condition. This practice induces immediately a skin created by fluids losses and prolong the flow back periods making the stimulation much less effective. Another methodology is to run through tubing guns and perforate in underbalanced conditions with smaller guns being limited by the completion size. In the latter case, the perforation performance are much less than the casing gun ones. In both cases, the full potential of the well is not achieved. A newer methodology is introducing re-perforation/perforation with casing guns in underbalanced, dry conditions, within snubbing operations. The methodology allows instantaneous gain of production and maximizes well recovery factor in the long term. Two pilot operations were executed with very good results and promising opportunities arise for candidate wells in the field.