Gas Hydrate System in Northern South China Sea and Numerical Investigation of Gas Production Strategy in Shenhu Area

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1 PETRAD-CCOP-PETROVIETNAM-VASI Seminar on Gas Hydrates 1-3 March 2011, Halong Bay, Vietnam Gas Hydrate System in Northern South China Sea and Numerical Investigation of Gas Production Strategy in Shenhu Area Nengyou WU 1,2,3, Shengxiong YANG 3, Haiqi ZHANG 4, Zheng SU 1,2, Keni ZHANG 5, George J. MORIDIS 5 1. GIEC, China; 2. GCGHR, China; 3. GMGS, China; 4. CGS, China; 5. LBNL, USA

2 OUTLINE q INTRODUCTION q GAS HYDRATE SYSTEM Dongsha area: concentrated hydrate Shen area: disseminated hydrate q NUMERICAL INVESTIGATION OF GAS PRODUCTION STRATEGY FOR THE HYDRATE DEPOSITS IN SHENHU AREA Production strategy Depressurization Huff-and-puff q CONCLUSIONS

3 Introduction pnational Project: Gas Hydrate Research in the North Slope of South China Sea( ,GMGS) pobjectives: To reveal the evidences for gas hydrate, including the geophysical, geological and geochemical indicators; To determine the distribution of gas hydrate; To evaluate the gas hydrate as the future new energy resources; To study the mechanism of gas hydrate formation.

4 Research Vessels R/V Haiyang 4, GMGS R/V Tanbao,GMGS R/V Fendou 5,GMGS R/V Sonne, RF, Germany SRV Bavenit, Fugro

5 Methods qgeophysical survey multi-beam mapping 2D/3D multi-channel high resolution seismic survey sub-bottom profiling heat flow measuring pseafloor observation with real-time imaging qgeological & Geochemical sampling and analysis qdrilling and coring

6 OUTLINE q INTRODUCTION q GAS HYDRATE SYSTEM Dongsha area: concentrated hydrate Shen area: disseminated hydrate q NUMERICAL INVESTIGATION OF GAS PRODUCTION STRATEGY FOR THE HYDRATE DEPOSITS IN SHENHU AREA Production strategy Depressurization Huff-and-puff q CONCLUSIONS

7 Case 1: Dongsha Area Carbonate Mountains Jiulong Methane Reef (Suess,Huang,Wu et al., 2005) Topographic Map of Survey Area showing the locations of Jiulong Methane Reef, Dongsha area

8 DSH-2-3: WD 857m DSH-2-2: WD 1064m DSH-2-1: WD 1147m DSH-4-1: WD 996m DSH-6-1: WD 1480m DSH-6-2: WD 1405m Topographic Features

9 Line HD173-1TA Seismic profile (SP ) seismic wave profile (SP )

叠加速度 (m/s) 1.25 1400 1500 1600 1700 1800 1.25 1400 1500 1600 1700 1800 1.25 1400 1500 1600 1700 1800 1.25 1400 1500 1600 1700 1800 1.50 1.50 1.50 1.50 双程 1.75 1.75 1.75 1.75 反 2.

10 叠加速度 (m/s) 双程反射时间 (s) (SP1846) (SP1806) (SP1766) (SP1726) Line HD174 velocity profile

118 35 118 47 118 59 119 10 22 20 DSH-5 区 DSH-1 区 DSH-3 区 22 08

DSH-6 区 DSH-4 区 21 56 水合物有利区水合物有利区钻探目标区钻探目标区建议井位建议井位 21 44 0 7.

11 DSH-5 区 DSH-1 区 DSH-3 区 DSH-2-3 井 DSH-2-2 井 DSH-2-1 井 DSH-2 区 DSH-4-1 井 DSH-6-1 井 DSH-6-2 井 DSH-6 区 DSH-4 区水合物有利区水合物有利区钻探目标区钻探目标区建议井位建议井位 (km) Topography, BSR Distribution, Proposed drilling sites in Dongsha area

12 Video-recorder of Jiulong Methane Reef from SO-177, a joint cruise between GMGS, China and IFM-GEOMAR, Germany

of fissures), Carbonate rock: 13 C = -56 per mil PDB

13 Jiulong Methane Reef, Carbonate rock with bacterial patches (yellow small irregular patches and white lining of fissures), Carbonate rock: 13 C = -56 per mil PDB indicates fully methane-derived carbon (Suess, Huang, Wu et al., 2005)

14 Clams with age of 11.2 ka, accompanied with the carbonate rocks (Suess, Huang, Wu et al., 2005)

15 Authigenic carbonates C & O Isotope value plotting of carbonates -10 This study 0 Normal marine Blake Ridge 996 Hydrate Ridge Okhotsk Sea δ 13 C PDB Methane-derived Carbonates or cold seeps carbonates δ 18 O PDB Note: The data of Blake Ridge 996,Hydrate Ridge, and Okhotsk sea from Naehr(2000),Greinert (2001), Esikov (1990), respectively.

16 Case 2: Shenhu Area GMGS-1 GH Drilling Expedition: April 21-June 12,2007 Vessel:SRV BAVENIT Contractor:Fugro Partner: Geotek Leg 1: April 21-May 18 Leg 2: May 19-June 12

17 Location of drilling site Tectonically in the Pearl River Mouth Basin Shenhu is in the middle of the north slope of the SCS between Xisha Trough and Dongsha Islands Pearl River Mouth Basin Tectonic subsidence since the middle Miocene high sedimentation rate. Sediment: m TOC: % source of oil and gas.

18 SH-2-5 SH-2-3 SH-2-4 SH-2-2 SH-2-1 SH-3-3 SH-3-2 SH-3-1 Topography, BSR Distribution, Proposed drilling sites in Shenhu area

20 SH-2-5 SH-2-3 SH-2-4 SH-2-2 SH-2-1 SH-3-3 SH-3-2 SH-3-1

21 Wire line logging Natural Gamma Gamma density Neutron Porosity Electrical resistivity Caliper Temperature In pipe logging Open hole logging below about mbsf

22 Long wire line piston corer FHPC ~7.5 m Short hammer corer FC ~3m Short Pressure Corers - FPC and FRPC ~1m In-situ Temp. Measuring & Porewater sampling Coring

23 Onboard analysis 1.Non-pressure core analysis: IR imaging, core processing and core logging; pore water squeezing, geochemistry and gas analysis 2.Pressure core analysis in cold van: X-ray imaging and logging

25 Wire line log at Site SH2 of Shehu Area, north slope of South China Sea Caliper V P R D R s

16-17 19-20 14 Temperature probe data SH3B-14C IR image showing the

26 Temperature probe data SH3B-14C IR image showing the cooling of core from dissociation of gas hydrate e.g. SH3B-14C Non-pressure core

27 Core temperature data also measured with probes, showing the cooling from gas hydrate dissociation e.g. SH2B 185mbsf Gas hydrate 229mbsf

28 pressure core SMCL-P SH2B 15P, higher velocity and lower density

29 Shallow geochemistry of pore waters of sediments showing the decrease of sulfate and the increase of methane at the sulfate-methane interface

30 Depth of SMI based on the variation of SO 4 2- and CH 4 concentrations of sediment pore-water from Shenhu Area Site Geographical position Latitude (N) Longitude (E) WD (m) SMI (mbsf) SH SH SH SH SH

31 Salinity, chlorinity, and sulfate concentration of pore waters of sediments from site SH2. Salinity and chlorinity are corrected for drill water infiltration

32 Gas composition data of void gases and pressure core gases for site SH2, including methane to ethane ratio (C1/C2) and ethane and propane content methane %; Ethane, propane very low; C1/C2 >1200 above 190 mbsf below 190 mbsf; Structure I gas hydrate

33 Correlation between sonic velocity, resistivity, temperature, hydrate concentration, porosity, clay content and coring at SH2 声波速度 (m/s) 电阻率 (OHM-M) 4 5 地层温度 ( C) 20 含天然气水合物层饱和度 (%) 孔隙水分析保压样品释压孔隙度及泥质含量 (%) 孔隙度泥质含量实测值 Coring 取芯方式 9C 10P 11C 12R 13C 14C 15P 16R 17C 18C 19P 20R 21C 22C 23C 24C 25C 取芯深度 H: 辉固液压活塞取芯 P: 辉固保压取芯取芯失败特征描述岩心低温异常,9-10 C 取芯失败岩心低温异常,9-10 C 保压样品含水合物岩心低温异常,1-2 C 取芯失败保压样品含水合物岩心低温异常,4 C 岩心低温异常,1-2 C 保压失败取芯失败岩心低温异常,4-5 C 岩心低温异常,-1-3 C 岩心低温异常,10-11 C 岩心低温异常,8-9 C 岩心低温异常,10-11 C R: 辉固旋转保压取芯

34 Correlation between sonic velocity, resistivity, temperature, hydrate concentration, porosity, clay content and coring at SH 声波速度 (m/s) 电阻率 (OHM-M) 地层温度 ( C) 饱和度 (%) 孔隙度及泥质含量 (%) 孔隙度泥质含量 Coring 取芯方式取芯深度特征描述含天然气水合物层 13P 保压样品含水合物 14C 岩心低温异常,14-16 C 15R 保压样品含水合物 TP 原位温度 C FPWS C: 辉固取芯 P: 辉固保压取芯 R: 辉固旋转保压取芯 TP: 原位温度测量 FPWS: 辉固孔隙水取样

35 Correlation between sonic velocity, resistivity, temperature, hydrate concentration, porosity, clay content and coring at SH7 声波速度 (m/s) 电阻率 (OHM-M) 地层温度 ( C) 饱和度 (%) 孔隙度及泥质含量 (%) 含天然气水合物层孔隙度实测值泥质含量 Coring 取芯方式取芯深度特征描述 9C 取芯失败 10C 11R 取芯失败保压样品含水合物 12C 取芯失败 13P 14P 保压失败保压失败 15R 保压样品含水合物 16C 17C(a) 岩心低温异常取芯失败 17C 岩心低温异常,10 C 18P 19C 保压失败岩心低温异常,-9 C 20C 岩心低温异常 21C 岩心低温异常 200 C: 辉固取芯 P: 辉固保压取芯 R: 辉固旋转保压取芯

36 The gas hydrate bearing sediments are silty clay, a kind of very fine sediment. From the sediments, the gas hydrate is not visualized. SH2B-15P SH7B-15R

37 XRD images of hydrate samples (400) I (410) I (411) I Ice (421) I (320) I Ice (430) I Ice (520) I Ice (321) I Ice (210) I (211) I Ice Ice (531) I (433) Ice I Ice (620) I I 型水合物衍射图谱 Structure I Hydrate typical image of Structure I hydrate SiO 2 Ice Ice (320) I CaCO 3 (400) I (420) I (421) I (510) I (521) I CaCO 3 Ice (433,530) I SH7B-15R-p SH2B-17C-b SH7B-15R-b2 SH7B-15R-b θ ( ) images of hydrate samples from Shenhu Area, SCS

38 δ 13 C PDB & δd VSMOW values of headspace methane from sediments at site SH2, showing that the gas source of gas hydrate is microbial 微生物 CO2 还原热成因 -300 醋酸根发酵 sample SH2B-12R SH3B-7P SH5C-11R SH3B-13P δ 13 C PDB δd VSMOW

39 gas hydrate concentration calculated from porewater freshening, hydrate-bearing sediment zone is located within 43 meters above the BSR

40 Gas Hydrate concentration profiles SH2B c very uniform hydrate layer disseminated gas hydrate very high concentration

41 Summary of hydrate drilling in Shenhu area, SCS: 8 sites investigated; 5 sites cored; 3 sites hydrate collected; hydrate layer m thick; Max. hydrate concentration 25-48% of pore volume SH7 25 m hydrate layer up to 44% SH3 10 m hydrate layer up to 25% SH2 43 m hydrate layer up to 48%

42 venting ocean Seafloor conc. Seafloor //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// Concentrated chimneys Free gas Diffuse hydrate layer BSR sediments Hydrate formation 1. Regional layer ~20-30 m thick above BSR disseminated hydrate: Shenhu Case, SCS 2. Localized channels or chimneys concentrated hydrate: Dongsha Case, SCS -upward fluid transport in fractures-faults

43 How does seafloor hydrate occur? 1.Widespread layer above base of stability (BSR) Usually large volumes but generally low concentrations; However high concentrations in Shenhu area, SCS --Probably difficult to produce? --Probably too deep for climate effect 2.Local structures ( chimneys seismic blank zones) Up to kilometers across, often very high concentrations --Best targets for production? --near or at seafloor so susceptible to climate change? --also seafloor gas plumes

44 The estimate of total amount of methane trapped in the drillingconfirmed 15 km 2 extent of the Shenhu hydrate deposit is about 16 B m 3 at a 50% possibility According to the resource assessment method of Gornitz & Fung(1994), Satoh et al.(1996), Collet & Ladd(2000), Milkov & Sassen (2003) Seismic, drilling, wire-line logging, geochemical data: gas hydrate occurrence 15km 2 thickness of GHBZ m porosity 55-65% hydrate concentration 20-48% 1 m 3 gas hydrate equals to 164 m 3 free gas

45 NUMERICAL INVESTIGATION OF GAS PRODUCTION STRATEGY FOR THE HYDRATE DEPOSITS IN SHENHU AREA Objective: to assess the production potentials from hydrate deposits in Shenhu area of SCS using numerical simulation

46 Shenhu hydrate deposits Drilling Site: SH2 Water Depth: 1235m Seafloor Temp.: 3.3 o C Hydrate Bearing Layer: mbsf Thickness of HBL: 43m Sediment Porosity: 36-40% Hydrate Concentration: 1-48% In-situ Pore Water Salinity: (Wu et al., 2008, Wu et al.,2010)

47 Classification of hydrate deposits CRITERIA: reservoir geology and initial conditions q q CLASS 1: Formation includes two zones The hydrate interval (bottom at hydrate stability) An underlying two-phase zone with mobile gas CLASS 2: Formation includes two zones The hydrate interval (at or above bottom at hydrate stability) An underlying single-phase zone of mobile water q q CLASS 3: Formation composed of a single zone Formation coincides with the hydrate interval Absence of a hydrate-free interval CLASS 4: Disperse oceanic hydrates without bounding formations (usually low S H )

48 Well design H Modified from Moridis et al., 2007 Focused on the hydrate deposits of Classes 2 that occurs in Shenhu Single Vertical well Constant rate by Depressurization No boundary Permeable and WZ To avoid gas escape and water flooding at early stage of production, screened interval = 1/3 H ~ 14m

49 Simulator and Numerical Model TOUGH+HYDRATE code [Moridis et al., 2005]: Describes the non-isothermal hydrate dissociation/formation, CH 4 flow, and phase behavior - Includes most recent information from validation using the Mallik field data Methane hydrates CH 4.N m H 2 0 = CH 4 + N m H 2 0(l,i), 5.75 N m 7.4 Second-gas hydrates (*) G.N G H 2 0 = G + N G H 2 0(l,i), G= C n H 2n+2,H 2 S, CO 2,N 2 Binary hydrates (*) c m [CH 4.N m H 2 0 ] c G [G.N G H 2 0], c m +c G =1 (*): Included but deactivated in TOUGH-Fx/HYDRATE

gridblocks in (r, z), of which 25,200 were

50 Geometry HBL: 40m overb. & underb. ~20 m are sufficient to provide accurate heat exchange same media properties discretized in (r, z) 105 x 242 = 25,410 gridblocks in (r, z), of which 25,200 were active very fine discretization r<20m Δz = 0.25 m In HBL, but coarser in the WZ equilibrium reaction of hydrate dissociation, 100,800 coupled equations

51 Initial condition Reference case SH2 site Thickness of HBL: 40m Hydrate Bearing Layer: mbsf Sediment Porosity: 38% Hydrate Concentration: 40% In-situ Pore Water Salinity: 30 Presumed permeability: 10mD Pressure: hydrostatic pressure Temperature: computed using T+H P W =3MPa HBL= 40m Φ= 38% S H = 0.4 K=10 md

52 NUMERICAL INVESTIGATION OF GAS PRODUCTION STRATEGY FOR THE HYDRATE DEPOSITS IN SHENHU AREA Hydrate Production by Depressurization

53 gas production rate and release rate Q PT : total CH4 and Q PG : free CH4 flow produced at the well, and (c) Q R :CH4 released from hydrates in the entire simulated domain Q PT, total gas production rate -- gas production rate is the absolute criterion for assessing gas production potential Inflection at t = 1300d Q PG, free gas flow rate Q PT ~ 463 m 3 /d Q PG ~ 348 m 3 /d attenuation Q R, gas release rate Q R ~ 157 m 3 /d Q PT ~ 3Q R << Q lim Q lim = m 3 /d

54 Cumulative Gas Volume V PT : total gas produced at well; V PG : free gas volume produced; V R : gas volume released from hydrate; V G : free gas remain in reservoir V PG, produced free gas V PT, total gas volume produced V R, gas released from hydrate V G, remaining in reservoir Total gas produced V PT much bigger than released from hydrate V PT = ST m 3 of CH4 is produced but practically only ST m 3 of CH4 is released from hydrate Hydrate is far from exhausted, 64% produced gas is from dissolved gas, but not hydrate Gas production and dissociation efficiency are very low

55 Water production and gas-to-water ratio Q W : water production rate; R GW : volumetric ratio of cumulative gas V PT to cumulative water V W produced at the well Q W = 86 ton/d=83.5 m 3 /d Q W, Water production rate jump R GW, production ratio of gas to water Inflection at t=1300d R GW < 7.5 Shows economical efficiency of gas production from the hydrate deposits. R GW falls rapidly from 30 at the initial point to 7.5 at the inflection point and drops to ~4.3 at the end of the production

56 S H Spatial Distribution Hydrate dissociation front receding radially Breaking through water Low gas production efficiency Water flooding water Showing the evolution of hydrate saturation S H during production from the vertical single well

S G Spatial Distribution Gas occur only in dissociated space Tail points the main point of dissociation front indicating the contours of free

57 S G Spatial Distribution Gas occur only in dissociated space Tail points the main point of dissociation front indicating the contours of free gas between the production well and the hydrate dissociation front. Left end connects the production well and right end is the dissociation front.

58 S T Spatial Distribution Cold point due to hydrate dissociation and colder water flooding Hot flow due to warmer water flooding Evolution of temperature T during production from the single vertical well

59 X inh Spatial Distribution salinity Water flow water invasion Gas zone gas flow becomes smaller Gas zone dissociation front Water flow Distribution of the salt concentration shows the dilution effect of dissociation on salinity during production from the single vertical by depressurization

60 NUMERICAL INVESTIGATION OF GAS PRODUCTION STRATEGY FOR THE HYDRATE DEPOSITS IN SHENHU AREA Hydrate Production by Huff-and-puff

61 Class 2: Well Configuration Concept Model for Thermal production Next period Injected water temperature: 80 o C

Production Scheme of 1-day production and 2-days injection 2 4 gas released from hydrate 1-day production 2-day injection Q PT <<Q R 1 5 much gas is released during production interval 3 secondary

62 Production Scheme of 1-day production and 2-days injection 2 4 gas released from hydrate 1-day production 2-day injection Q PT <<Q R 1 5 much gas is released during production interval 3 secondary hydrate forms much gas forms hydrate during the injection interval volume of gas produced at the well = 400 m 3 volume of gas released from hydrate = 1196m 3 volume of gas forming secondary hydrate = 1060 m 3 in one period

63 OUTLINE q INTRODUCTION q GAS HYDRATE SYSTEM Dongsha area: concentrated hydrate Shen area: disseminated hydrate q NUMERICAL INVESTIGATION OF GAS PRODUCTION STRATEGY FOR THE HYDRATE DEPOSITS IN SHENHU AREA Production strategy Depressurization Huff-and-puff q CONCLUSIONS

64 Conclusion 1 gas hydrate system of Northern SCS There are two kinds of gas hydrate formation in SCS: disseminated hydrate-shenhu and concentrated hydrate-dongsha High concentrations of hydrate in a disseminated forms discovered in the very fine-grained sediments in shenhu Area, SCS

65 Conclusion 2 depressurization gas production rate decreases and has a drop when hydrate seal is broken through at t = ~3.5 yr., water production rate increases and has a jump at the same time. average gas production rate = 463 m 3 /d, average gas release rate =157 m 3 /d, average water production rate = 86 t/d, average gas production ratio = 4.2

66 Conclusion 3 huff-and-puff Injecting hot water was not an effective way to dissociate hydrate. Most gas released was due to depressurization during production intervals. Much gas converted to secondary hydrate during hot water injection because of the pressure increasing

67 Thank you for your attention!

Watered-out Reservoir Parameter Interpretation Research of Xingnan oilfield Development Area

IOSR Journal of Engineering (IOSRJEN) ISSN (e): 50-1, ISSN (p): 78-8719 Vol. 05, Issue 1 (December. 015), V PP 8-88 www.iosrjen.org Watered-out Reservoir Parameter Interpretation Research of Xingnan oilfield