Abstract
Many oilfields in Russia and CIS countries are in late development stage with waterflooding being deployed for decades. Most of these fields have rapidly increasing watercut, decreasing injectivity and productivity. Various methods of production optimization are used including well stimulation techniques – conventional and novel. One of relatively new technologies is the wave stimulation when the wellbore and reservoir are treated by acoustic, seismic or other type of wave generated by different tools.
These technologies have short treatment time, simple-to-use tools and work in different formations and wells. Tool placement (wellhead or downhole), wave frequency and generated energy differentiate methods. In this paper we focus on seismic impact well treatment when the wave generator is installed at wellheads. Energy is generated on the surface with compressed gas, released into well instantaneously. Shock wave propagates through liquid-filled well column and transforms into seismic wave in-situ. This allows scale and deposits removal in wellbore and near-wellbore area, positive modification of injection or production profile. Deeper in reservoir, seismic wave propagates at high velocity and mobilizes oil trapped behind natural flow barriers.
The impact of seismic wave stimulation on permeability restoration and improvement, water injection profile and oil displacement have been modeled in laboratory experiments and modeled with the software. Few generations of tools have been used in the field operations. Recently, seismic stimulation has been combined with chemical treatment: acid, alkaline, surfactant, gas-generating agents or combination of these. Mechanistic supplement of chemical injection allows deeper and uniform distribution of chemical agent and larger contact zone. There is some synergy between seismo-chemical stimulation and enhanced oil recovery (EOR) methods. To date, injection and production wells (both vertical and horizontal) have been treated in various fields across Russia, Europe and Asia. There is a large range of temperature, salinity, perforation interval of treated wells; formation depth in these fields is up to 3.5 km, reservoir permeability from 5 mD. On average, stimulation of injectors increased injectivity by 85% for 18 months that led to incremental oil rate of 30% in treated pattern (around 45,000 bbl/treatment). Averaging producers’ treatment results gives 65% increase in oil rate (total 12,000 bbl/treatment), effect lasting for 22 months. Typical unit technical cost (UTC) in these operations was below 2$/bbl. As a rule of thumb, seismo-chemical treatments have larger UTCs and deliver higher increase in injectivity and productivity indices.
The mechanisms, experimental procedures, field application history of seismic and seismo-chemical well stimulation are reviewed and presented. With around 250 wells treated, there is a high success rate and oil production increase. New generation of this improved oil recovery (IOR) technique combines benefits of mechanistic well stimulation, acid and/or chemical enhanced oil recovery.
