Slide 1 SPE-190844-MS Sulphate In Original Reservoir Chalk Rocks: Release Of Sulphate By Desulphated Sea Water And Effects On Wettability Ingebret Fjelde IRIS, University of Stavanger, National IOR Center of Norway
Slide 2 Sea water (SW) injection in chalk reservoirs • Pressure support and good recovery, but SW can cause • Reservoir souring • Scale deposition • Weakening of chalks • Desulphated sea water (D-SW) • Lower sulphate concentration and may reduce problems • Also Ca 2+ and Mg 2+ reduced and Ca 2+ /Mg 2+ -ratio increased SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 3 Objectives • Investigate formation damage potential and release of sulphate when injection water changed from SW to D-SW in reservoir chalk • Effects of low sulphate concentration as in real FW, on spontaneous imbibition and viscous flooding of reservoir chalk SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 4 Injection brines to reservoir chalk FW SW D-SW SRPW Element/ion (mmol/l) (mmol/l) (mmol/l) (mmol/l) Al ------ ------ ------ <0.002 Ba ------ ------ ------ 0.0004 Na + 996.1 457.2 414.1 ------ K + 5.29 10.00 8.72 9.21 Ca 2+ 28.94 10.55 0.85 4.24 Mg 2+ 7.78 53.36 1.77 10.29 Ca 2+ /Mg 2+ 3.72 0.19 0.48 0.41 S ------ ------ ------ 0.212 Si ------ ------ ------ 0.024 Sr ------ ------ ------ 0.029 2- SO 4 0.510 22.955 0.177 0.198 Cl - 1064.5 546.8 426.3 ------ HCO 3 - 9.26 2.33 1.38 ------ D-SW prepared based on recipe from a sulphate removal plant SRPW sample received from a sulphate removal plant SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 5 Injection of brines to reservoir chalk • Reservoir plugs cleaned by toluene/methanol and dried with N 2 -gas • Brine injection • Differential pressure (dP) • Effluent analyzed for sulphate, pH and elements SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 6 FW/D-SW/SRPW (CP1) • FW → D-SW, i.e. injection of D-SW where SW not injected dP No formation damage SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 7 FW/D-SW/SRPW (CP1) Sulphate release Sulphate Injection FW without sulphate (Fjelde 2008) 340mg/l = 3.54mmol/l • FW sulphate release • D-SW first step → sulphate peak • SRPW after aging, small sulphate peak • SRPW low pH (pH=5.6) as injected SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 8 FW/D-SW/SRPW (CP1) pH • D-SW higher than injected • SRPW much higher than injected SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 9 FW/D-SW/SRPW (CP1) Elements Ca and Mg Ba and Sr Ca-peak and Mg low in same period as Ba and Sr produced sulphate peak SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 10 FW/D-SW (CP2) Sulphate and pH pH Sulphate • FW peak but stabilized • D-SW higher than injected • D-SW • First D-SW, peak • After aging, smaller peak • Similar as plug CP1 SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 11 FW/D-SW (CP2) Elements Ca and Mg Ba and Sr Ca peak and low Mg when sulphate peak Sr and Ba high Interactions similar in CP2 and CP1 SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 12 SW/D-SW (CP3) • From SW to D-SW, i.e. injection of D-SW where SW has been injected dP pH No formation damage D-SW high pH SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 13 SW/D-SW (CP3) Elements Ca and Mg Ba and Sr Ca and Mg close to injected Ba and Sr low, but higher than injected SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 14 D-SW/SW (CP4) • Injection SW when D-SW not necessary because brine will not reach producers dP No formation damage SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 15 D-SW/SW (CP4) Sulphate and pH Sulphate peaks during D-SW SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 16 D-SW/SW (CP4) Elements Ca and Mg Ba and Sr Ca-peak in same period as sulphate peaks Ba and Sr higher than injected SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 17 Effect of initial sulphate on oil recovery • Reservoir chalk plugs (Field 2) prepared with and without sulphate in FW • Spontaneous imbibition (SI) experiments earlier reported (Fjelde & Asen, 2015) • Viscous flooding experiments with SW after SI SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 18 Effect of initial sulphate on recovery / Spontaneous imbibition • Earlier reported (Fjelde and Asen, 2015) S o vs time • SI higher when initial sulphate present than without initial sulphate • i.e. more water-wet in presence of initial sulphate than without initial sulphate SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 19 Effect of initial sulphate on recovery / Viscous flooding • After SI • Without initial sulphate • Slow production and S o low • Extra oil when rate increased • With initial sulphate • Production ended earlier • Minor extra oil when rate increased • More water-wet when initial sulphate • Spontaneous imbibition • Viscous flooding SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 20 Brine compositions • Composition SRPW can vary • Important to evaluate formation damage and sulphate release within expected range • Brine composition important for oil recovery in chalk • SW improved spontaneous imbibition in reservoir chalks without initial sulphate (e.g. Fjelde and Asen, 2009; Webb et al., 2005) • Even though SRPW instead of SW can reduce problems, it is important that oil recovery is not reduced • Reservoir chalk preparation important • FW with low sulphate as in real FW, gave more water-wet reservoir chalk than FW without sulphate • Important to prepare core plugs with the correct amount of initial sulphate SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 21 Conclusions • Injection of SRPW to reservoir chalk • No formation damage (FW → D-SW/SRPW, D-SW → SW, and SW → D-SW) • Sulphate released during D-SW/SRPW injection • Effluent pH increased during SRPW injection • When sulphate peaks D-SW/SRPW injection, Ca-, Ba- and Sr- peaks while Mg low • Initial sulphate gave more water-wet reservoir chalk than without initial sulphate • Spontaneous imbibition of SW higher with than without initial sulphate • Viscous flooding production profile • Even though SRPW can reduce problems as reservoir souring, sulphate scaling and chalk weakening, it is important that recovery is not reduced • Important to prepare reservoir chalk with correct concentration of initial sulphate SPE-190844- MS • Sulphate in Original Chalk Rocks …. • Ingebret Fjelde
Slide 5 Acknowledgements Ingebret.fjelde@norceresearch.no Ingebret.Fjelde@uis.no
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