Single Well Chemical Tracer Testing (SWCTT) is traditionally performed to determine oil saturation after waterflooding and after enhanced oil recovery techniques. Raudhatain Lower Burgan (RALB) and Sabriyah Lower Burgan (SALB) SWCTT oil saturation reduction due to injection of surfactant-polymer and alkali-surfactant solutions, respectively, were 7 and 8% OOIP, respectively. During SWCTT, injection rate and surface pressure are routinely measured for each injected solution. Injection rate and surface pressure permit additional determinations to be made as outlined below:

  1. Pseudo resistance factor to any fluid "i" can be calculated and, from this, changes in injectivity can be determined

  2. Flowing viscosity of injected fluids relative to water

  3. Effective permeability to injected fluids

  4. Injectivity factors

Pseudo resistance factor for RALB continually increased with seawater injection, from 0.5 to 1.0 indicating a reduction of kwro to approximately half and a twofold loss of injectivity. SALB kwro showed a three-fold loss of injectivity with seawater injection (pseudo resistance factor increased to 1.0 from 0.36). RALB pseudo residual resistance factor was 6.0 indicating a six-fold loss of injectivity due to surfactant-polymer and polymer drive solution injection even though the oil saturation was reduced by 7% OOIP. SALB pseudo resistance factor increased to 1.7 during alkaline-surfactant solution, indicating a loss of injectivity and an increase in flowing viscosity. SALB pseudo residual resistance factors were 0.89 to 1.06 suggesting no damage to reservoir rock and no loss to a slight increase of injectivity or an increase of kwro after an 8% OOIP saturation reduction. RALB surfactant-polymer rheometer viscosity was 0.55 cP while flowing viscosity was 0.21 cP as calculated from pseudo resistance factor data with the comparative polymer drive solution viscosities being 1.9 cP rheometer and 0.16 cP flowing. SALB alkaline-surfactant solution flowing viscosity was calculated to be 0.80 cP compared to water viscosity of 0.50 cP. Calculated SALB kwro values for injection of water, alkaline-surfactant, and water flush after alkaline-surfactant are 0.012, 0.007, and 0.011 to 0.015mD, respectively. Calculated RALB kwro values for injection of seawater and seawater flush after surfactant-polymer/polymer flush are 0.019 and 0.004 mD.

Keywords:
enhanced recovery, effective water permeability, pseudo resistance factor, upstream oil & gas, chemical injection, oil saturation, chemical flooding methods, swctt, resistance factor, injection rate
Subjects:
Improved and Enhanced Recovery, Waterflooding, Chemical flooding methods
Copyright 2019, Society of Petroleum Engineers
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