Abstract

Severe fluid loss problems was experienced in Mumbai High and Bassein lime stone in Neelam, mainly due to pressure depletion consequent to sustained production from the layers. Loss problem in producing zones are presently being controlled with imported pills which contain some solid materials and poses multiple problems during work over operations like retrieval of packer etc. WSS Ahmedabad has made an in-house efforts to develop a solid free pill which can develop high viscosity in the producing zone and form a plug like structure to prevent losses and having thermal stability for minimum 120 hrs or till work-over job completed at 120°C and no residue after the job

Fresh cross linked gel was prepared by using various additives as per the field conditions and stability of the cross linked gel was optimized. Using HPHT filter press, the wall building coefficient ‘Cw’ and spurt loss ‘Vsp’ were calculated for cross linked polymer under different conditions. Disintegration of cross linked gel with different concentration of HCl, acetic acid & suitable gel breakers were optimized. Series of experiments were carried out for delay time v/s thermal stability for proper placement of pill at target zone.

The clean pill has been designed with available indigenous chemicals and biodegradable polymer. The pill develops high viscosity in the thief zone and forms a plug like structure. The crosslinking of the plug can be controlled by optimizing the dosage of delaying agents to allow for its easy placement. The designed cross linked pill may be self-degraded after 6-7 days at reservoir temperature. Pill can also be easily disintegrated in mild HCl. (if required) and can be flowed back after the completion of work over job, without damaging the producing zone

The X-linked polymer plug is dependable well control method for safely isolating the producing zone during well service operations. The X-linked polymer plug so developed is envisaged for its field trial. The paper describes the results of intensive lab studies and execution methodology for the development of a solid free, thermostable, biodegradable X-linked polymer plug which can be used as temporary isolation in Mumbai offshore. The newly developed polymer plug may prove to be an indigenous & cost effective thermosetting polymer plugs. the successful field trial will be extremely beneficial for isolating the thief zones in lime stone reservoirs where this phenomenon is very common and different type of products by different companies have tried with mixed results

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