WATERFLOOD RECOVERY EFFICIENCY Reservoir Wettability, Connate Water And Improved Recovery Through Manipulation Of Injection Brine Composition Norman R. Morrow J. E. Warren Distinguished Professor Department of Chemical & Petroleum Engineering University of Wyoming
WATERFLOODING Accounts for more than 50% of current US Oil Production Has been highly successful for more than 60 years Improved oil recovery by waterflooding has worldwide importance.
100 80 brine S wi = 20% core Oil Recovery 60 40 20 TARGET FOR TERTIARY RECOVERY OIL RECOVERY BY WATERFLOOD 0 0 5 10 15 Injected Brine Volume (PV) WATERFLOOD (Forced Imbibition)
10 STRUCTURE OF RESIDUAL OIL TRAPPED IN VERY STRONGLY WATER-WET SANDSTONE 100
STRUCTURE OF RESIDUAL OIL TRAPPED IN BEAD PACK NOTE AREAS OF SOLID/OIL CONTACT
TERTIARY RECOVERY BY SURFACTANT FLOODING MOTIVATION: More Oil A Large Market for Chemicals (Upstream/downstream synergy within integrated companies?) Field results were disappointing WAS RESERVOIR RESIDUAL OIL OVER ESTIMATED?
Number of tests (2% intervals) 1978 CUT OFF FOR TERTIARY RECOVERY~28% 36% OF TESTED RESERVOIRS Residual Oil, percent RESIDUAL OIL SATURATION AFTER WATERFLOODING ( MEASURED BY THE SINGLE-WELL TRACER TEST - 117 RESERVOIRS) ALL RESERVOIRS HAD BEEN WATERFLOODED AND WERE POTENTIAL CANDIDATES FOR TERTIARY RECOVERY
Optimum conditions for oil recovery? The assumption (widely believed) that most reservoirs were strongly water-wet and this was best for recovery came into question. What is the flow mechanism that gives low residual oil saturations?
35 RESIDUAL OIL SATURATION: % 30 25 20 15 10 5 Core Data: East Texas Field = 27.0% K = 354 md Extracted with Benzene and Methanol 0 1 2 3 4 5 WATERFLOOD SEQUENCE INCREASE IN RESIDUAL OIL SATURATION GIVEN BY A SERIES OF WATERFLOODS ON A FRESH CORE (After Richardson & Perkins, 1955)
OIL WATER OIL IDEALIZED EXAMPLES OF CONTACT ANGLES AND SPREADING
OIL RECOVERY (% OOIP) Strongly Water-Wet, S wi = 16% Strongly Oil-Wet Sandstone S wi = 9% WATER INJECTED (PV) WATERFLOOD RECOVERY FROM STRONGLY WATER-WET AND STRONGLY OIL-WET SANDSTONE (After Raza et al, 1968)
OIL RECOVERY (% OOIP) DECREASING WATER WETNESS WATER INJECTED (PV) CHANGE IN OIL RECOVERY WITH WETTABILITY AS DEFINED BY THE US BUREAU OF MINES CENTRIFUGE TEST (Donaldson et al 1969)
80 OIL RECOVERY (% OOIP) 70 60 50 40 30 20 10 0 O 47 O 90 O 138 O 180 O 0 0.1. 2. 3.4.5. 6 WATER INJECTED (PV).7.8.9 1.0 EFFECT OF WETTABILITY ON WATERFLOOD PERFORMANCE (After Owens & Archer, 1970)
OIL RECOVERY (% OOIP) STRONGLY WATER-WET (Refined Oil) MIXED WETTABILITY (Film Deposited from East Texas/Heptane - Refined Oil) WATER INJECTED (PV) MIXED WETTABILITY (ADSORBED FILM) VS. STRONGLY WATER-WET (After Salathiel, 1973)
DISTRIBUTION OF WETTING AND NON-WETTING PHASES AT LOW WETTING PHASE SATURATION
AREAS OF CONTACT: OIL/WATER; OIL/SOLID AND WATER/SOLID
OIL RECOVERY (% OOIP) STRONGLY WATER-WET (Reservoir temp. and live crude oil) WEAKLY WATER-WET (Conventional-ambient temp.) WATER INJECTED (PV) RESERVOIR CONDITIONS VS. CONVENTIONAL TEST (After Kyte et al, 1961)
OIL RECOVERY (% OOIP) WEAKLY WATER-WET (Moutray Film - Refined Oil) STRONGLY WATER-WET (Refined Oil) ESTIMATED WATER INJECTED (PV) MIXED WETTABILITY (ORGANIC FILM ADSORBED FROM MOUTRAY CRUDE) (After Morrow et al. 1986)
OIL RECOVERY (% OOIP) WEAKLY WATER-WET (Fresh Core - Refined Oil) STRONGLY WATER-WET (Cleaned Core - Refined Oil) WATER INJECTED (PV) CLEANED VS. FRESH RESERVOIR SANDSTONE (After Rathmell et al. 1973)
OIL RECOVERY (% OOIP) WEAKLY WATER-WET (Loudon - aged one year) STRONGLY WATER-WET (Loudon - no aging) WATER INJECTED (PV) EFFECT OF TIME OF CONTACT WITH LOUDON CRUDE OIL (After Wang, 1986)
RELATIVE RECOVERY FACTOR MOUTRAY FILM (1986) LOUDON CRUDE (1986) FRESH CORE (1973) STRONGLY WATER-WET CONVENTIONAL CORE (1959) BETTER THAN VERY STRONGLY WATER-WET WORSE THAN VERY STRONGLY WATER-WET WATER INJECTED (PV) DISPLACEMENT EFFICIENCY (RELATIVE TO STRONGLY WATER-WET CONDITIONS)
OIL WATER FUSED GLASS SURFACES Very strongly waterwet oil (black area is oil retained mainly in pore bodies as blobs) Weakly water-wet-oil tends to be displaced from the pore bodies to give low residual oil saturation
WETTABILITY CHANGE INDUCED BY CRUDE OIL Depends on: the rock the crude oil the brine the initial water saturation the aging temperature the aging time displacement temperature crude oil/brine/rock interactions
I w = S ws S wf oven 100 % brine core oil brine S w 50 % core 1 0% Time, t SPONTANEOUS IMBIBITION
AMOTT WETTABILITY INDEX Centrifuging or waterflooding is used to measure forced displacement S of. The Index to water is defined by: I w = S ws S wf
100 OIL RECOVERY (% OOIP) 80 60 40 20 20 PV 5 PV 3 PV 1 PV BT 0-1.0-0.5 0.0 0.5 1.0 I w-o OIL RECOVERY VS. WETTABILITY
OIL RECOVERY AND BRINE COMPOSITON
OIL RECOVERY (% OOIP) Brine 1 (4% NaCl + 0.5% CaCl 2 ) Brine 2 (2% CaCl 2 ) BRINE INJECTED, PV RECOVERY OF PRUDHOE BAY CRUDE OIL BY WATERFLOODING WITH BRINES OF DIFFERENT COMPOSITION (After Yildiz et al., 1999)
OIL RECOVERY (% OOIP) BRINE 1 ONLY INCREASE(injection of Brine 1) BRINE 2 ONLY Brine 1 (injected) Brine 2 (initial) BRINE INJECTED, PV MIXED BRINE WATERFLOODS WITH BRINE 2 AS CONNATE BRINE AND BRINE 1 AS INJECTION BRINE
OIL RECOVERY (% OOIP) BRINE 1 ONLY DECREASE (injection of Brine 2) BRINE 2 ONLY Brine 2 (injected) Brine 1 (initial) Recovery 56.9% OOIP S or = 32.4% BRINE INJECTED, PV MIXED BRINE WATERFLOODS WITH BRINE 1 AS CONNATE BRINE AND BRINE 2 AS INJECTION BRINE
ta= 240 hr. LESS 72 48 WATER-WET 24 R im (OOIP) ta = 0 hr. 4 48 R wf (OOIP) 1 0 12 6 4 72 240 LESS WATER-WET Imbibition time (min.) Brine injected (PV) IMBIBITION WATERFLOOD
100 CS Crude Oil/CS Brine/Berea 90 80 70 Rwf (% OOIP) 60 50 40 30 20 S wi =23-27 % T a =55 C t a =7.0 days T d =55 C connate=invading 0.01CSRB 0.1CSRB CSRB 10 Flood rate=10 ft/d 0 0 5 10 15 Injected Water Volume (PV) EFFECT OF DILUTION OF BOTH CONNATE AND INVADING BRINES ON OIL RECOVERY BY WATERFLOODING
Rim (% OOIP) 100 90 80 70 60 50 40 30 20 10 0 CS Crude Oil/CS Brine/Berea S wi =24-26 % T a =55 C t a =7.0 days T d =55 C VSWW curve connate=invading 0.01 CSRB 0.1 CSRB CSRB 1 100 10000 1000000 Dimensionless Time, t D k t L 2 o w c EFFECT OF DILUTION OF BOTH CONNATE AND INVADING BRINES ON THE RATE OF SPONTANEOUS IMBIBITION
100 90 CS Crude Oil/CS Brine/CS Sandstone CSRB=connate 80 70 Rwf (% OOIP) 60 50 40 30 20 10 invading brine CSRB 0.01 CSRB S wi =25% T a =55 o C t a =10 days T d =55 o C flood rate=6ft/d 0 0 1 2 3 4 5 6 7 8 9 10 11 Injected Brine Volume (PV) EFFECT OF THE CONCENTRATION OF INJECTION BRINE ON WATERFLOOD RECOVERY FOR RESERVOIR CORE
100 CS Crude Oil/CS Brine/CS Sandstone ) 90 80 70 60 50 40 30 20 10 0 CS RB 0.1 CS RB S wi =23.6% T a =55 o C t a =10 days T d =55 o C flood rate=3 fr/d 0.1 CS RB (Ca/Na 10X increased) 0 10 20 30 Injected Brine Volume (PV) EFFECT OF INJECTING DILUTED RESERVOIR BRINE FOR A MATURE WATERFLOOD
NO SENSITIVITY TO SALINITY WAS OBSERVED IF: the oil phase was a refined oil if the core did not contain an initial water saturation if the core was fired and acidized in order to destroy the kaolinite clay structure. (Tang & Morrow, 1999)
NECESSARY CONDITIONS FOR SENSITIITY OF OIL RECOVERY TO BRINE COMPOSITION Adsorption of polar components from crude oil the presence of connate water The presence of clay (kaolinite)
adsorbed polar oil components water oil oil oil clay clays solid water a. adsorption onto clay surface b. clay particle Adsorption of Polar Components from Crude Oil and Mobilized Clay Particles at Brine/Oil Interface
transition towards increased water-wet mobilized mixed-wet clay particles water oil solid water-wet clay particles Effect of Clay Wettability on Retained Oil
water oil retained oil water solid a. retained oil before dilute brine flooding b. retained oils become mobilizeed due to detached clay particles Detachment of Mixed-Wet Clay Particles and Mobilization of Oil Drops
FIELD APPLICATIONS Injection of selected brine at the beginning of a waterflood Change injection brine during the course of a mature waterflood Decide if produced brine (initially the reservoir connate brine composition) should be reinjected Each situation should be carefully tested in the laboratory at reservoir conditions. The type of results that have been shown provide guidance in selection of brine composition, but recovery efficiency may depend on competing interactions for specific situations.
CONCLUSIONS Most reservoirs have mixed wettability Oil Recovery is optimum at weakly water wet conditons Residual oil saturations achieved by waterflooding are usually too low for tertiary recovery to be economic even at high oil prices Laboratory studies show that recovery of crude oil is sensitive to the composition of the connate brine and injection brine Increase in oil recovery by waterflooding was obtained in the laboratory by injection of low salinity brine Much remains to be learned about the mechanism of oil recovery by waterflooding and the role of brine composition in crude oil/brine/rock interactions
SPE DISTINGUISHED LECTURER SERIES is funded principally through a grant of the SPE FOUNDATION The Society gratefully acknowledges those companies that support the program by allowing their professionals to participate as Lecturers. And special thanks to The American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME) for their contribution to the program.
Acknowledgements Support for this work was provided by: National Petroleum Technology Office (US Department of Energy) Enhanced Oil Recovery Institute-University of Wyoming ARCO, BP/Amoco (U.K./U.S.A.), Chevron, ELF/Total/ Gas de France/Institut Français du Pétrole (France), Exxon/Mobil, JNOC (Japan), Marathon, Phillips, Shell (The Netherlands), Statoil (Norway)