THE ANALYSIS OF GEOTHERMAL FIELD CHARACTERISTICS IN SICHUAN BASIN OF CHINA

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1 TE ANALYSIS OF GEOTERMAL FIELD CARACTERISTICS IN SICUAN BASIN OF CINA ZOU Xixiag, WANG Xube, YANG Shaoguo, YU uii, ad ZENG Yi Chegdu Uiversity of Tehology, Sihua, Chegdu, 60059, People s Republi of Chia Key wards: Geothermal field, heat flow, temperature log data orretio, Sihua Basi ABSTRACT Basi o the seletig thermal logs of 8 wells from 368 measurig temperature wells of oil field, we have established the geothermal distributio i Sihua Basi of Chia. For those usteady-state temperature log data, we have give a statistial aalysis orretig method. With the orreted temperature data we have established the geothermal distributio at depth from 000 m to 6000 m. Viewig these geothermal distributio, we fid the followig geothermal field harateristis i this Basi. The geo-temperature distributios i the shallow rust ad the average geothermal gradiet of sedimetary over i Sihua Basi show that the geo-temperature distributio i sedimets are essetially otrolled by the form ad udulatio of the upper Triassi ad the pre-siia rystallie basemet surfae. igher geotemperatures are loated i the areas of elevated basemet, suh as the middle uplift ad the southwester uplift, whereas lower temperatures are loated i the areas of depressed basemet, suh as the orthwester sag or the easter high folded belt. Usig alulatig ad estimatig method aordig to data, we have obtaied the terrestrial heat-flow i the Basi. The values rage from 35 to 80 mw/m, with a mea value of 6.44mW/m. For that ukow well shutdow time, we have referred a ew method to orret the temperature data as followig.. Corretio Fator By usig bottom hole temperature (BT) ad oil layer steadystate temperature (OLST), ad oil layer usteady-state temperature (OLUT), we a get oe orretig fator. G = BT BT. () OLST OLUT 3 Suppose that G satisfy G = A0 + A d + Ad + A3d, where d is the orrespodig depth, we a obtai A 0, A, A, A 3 from the statistial aalysis at study area.. Calulatig the Corretig Value of BT ( BT ) We use the followig formula to alulate the BT BT = BT G d () + d is the orrespodig bottom depth of the well..3 Calulatig Thermal Gradiet For. INTRODUCTION Sihua basi is loated at the southwester of Chia. For the eeds of oil ad gas exploratio there are about 400 systematially temperature loggig wells ad more tha 500 poit temperature loggig data iludig bottom hole temperature (BT) ad oil layer steady-state temperature (OLST) ad oil layer usteady-state temperature (OLUT) distributig i the Basi. Amog them, the deepest well is well Guaiig (700 m), while there are 9 wells for their depth at about m ad 0 wells at about m. The otiuous temperature logs were ormally measured at depth regioal of 000 m 4000 m. Basi o the seletig thermal logs of 8 wells from 368 measurig temperature wells of oil field, we have established the geothermal distributio i Sihua Basi of Chia. There 7 wells are high quality for a log period of well shut dow, iludig temperature gradiet measuremet of 4 wells ad 48 measured at early stage of oil produtio. The other 56 wells are temperature data of omprehesive logs. The terrestrial heat-flow values rages from 35 to 80 mw/m, with a mea value of 6.44mW/m.. CORRECTION OF TEMPERATURE LOG DATA BT = T N 0 + G (3) = is the stratum thikess, G is temperature gradiet, T 0 is temperature of the isothermal belt, suggestig that there are temperature logs M ad strata N, we have the system of equatio: M M N BTi T0) = i= i = = ( G (4) B = G (5) i i i i =(i,) represet the depth of well i ad stratum ; G=(G,G,...G N ) T ; B = [BT i -T 0 ] T. We a obtai the gradiet values G from the resolutio of the system equatio ad the ould alulate the temperatures at ay depth..4 Geothermal Distributio With the orreted temperature data ad steady-state 03

2 systematially temperature loggig data we have established the average geothermal gradiet of the over layer ad the the geothermal distributio at depth from 000 m to 6000 m. Viewig these geothermal distributio, we fid the followig geothermal field harateristis i this Basi. The geotemperature distributios i the shallow rust ad the average geothermal gradiet of sedimetary over i Sihua Basi show that the geo-temperature distributio i sedimets are essetially otrolled by the form ad udulatio of the upper Triassi ad the pre-siia rystallie basemet surfae. igher geotemperatures are loated i the areas of elevated basemet, suh as the middle uplift ad the southwester uplift, whereas lower temperatures are loated i the areas of depressed basemet, suh as the orthwester sag or the easter high folded belt. 3. TERRESTRIAL EAT FLOW 3. Stratum Rok Codutivity k d d d k = D( ) k k k D = d + d d k, k... k; d, d,... d are the mea thermal odutivity ad the aumulated thikess for eah lithologi respetively. There are two high K strata i the Basi. Oe is the Th - T ad the other is the Z. (6) 3. Calulatig ad Estimatig eat Flow Calulatig heat flow Oe dimesio steady state: q = kg (7) Estimatig loal area heat flow by usig the least square proedure. z dz T ( z) = T0 + q (8) z0 k( z) If k is ostat i eah strata so T ( z) = T0 + q( ) (9) k k k ad if the umber of measured data is m so there are ( i, ) Ti ( z) = T0 + q (0) k = For i=,... m; =,,... We a obtai the heat flow q aordig to the least square proedure: mi ( i, ) m S = mi [ Ti ( T0 + q )] () i= = k 3.3 The Charateristis of eat Flow i Sihua Basi The terrestrial heat-flow values rages from 35 to 80 mw/m, with a mea value of 6.44mW/m. Relatioship betwee heat flow ad the struture has the same harateristis as the geotemperature at spatial distributio. CONCLUSION The geothermal distributios i the shallow rust ad the average geothermal gradiet of sedimetary over i Sihua Basi show that the geothermal distributio i sedimets are essetially otrolled by the form ad udulatio of the upper Triassi ad the pre-siia rystallie basemet surfae. igher geothermal poit are loated i the areas of elevated basemet, suh as the middle uplift ad the southwester uplift, whereas lower temperatures are loated i the areas of depressed basemet, suh as the orthwester sag or the easter high folded belt. This distributio idiates that the terrestrial heat flow is redistributed durig flow from deep to shallow part of the earth. By meas of alulatig or estimatig about 00 terrestrial heat flow values distributig i the Basi we kow that the Basi is a stable sub-tetoi uit. The terrestrial heat-flow values rages from 35 to 80 mw/m, with a mea value of 6.44mW/m, whih has the same harateristis as the geotemperature at spatial distributio. ACKNOWLEDGMENTS This proet is supported by State Natural Siee Foudatio of Chia. The authors are also grateful to Professors Wag Jiyag, Wag Jia, Xiog Liagpig, Wag Ju, ad Ji Xi for their providig some data ad givig us a lot of helps. REFERENCES Wag Jiyag, Yag Shuzhe & She Jiyig, 988. Deep geothermal harateristis ad history of heat evolutio, uabei area. I Che Maixiag (editor), Geotherm i uabei area, Sietifi Press, 00-4, i Chiese. Wag Jia, Wag Jiyag, Xiog Liagpig, et al, 99. Geothermal harateristis of the Liaohe grabe ad their relatioship to oil-gas resoure, Bulleti of Istitutio of Geology, Chiese Aademy of Siee, Sietifi Press, 5, - 77, i Chiese. Wag Ju, uag Shagyao, uag Gesha, & Wag Jiyag, 990. Basi Charateristis of the Earth s Temperature Distributio i Chia, Seismologial Press, i Chiese. 04

3 Table Stratigraphi heat odutivity, k, i Sihua Basi Stratigraphi uit Maor lithologiss k (W/m K) Num. of samples Cretaeous (K) Sadstoe, mudstoe.03 6 Group Shaximiao of Sadstoe, mudstoe Jurassi (J) Group Zhiliuig of Sadstoe, sady mudstoe Jurassi (Jt) Group Xuiahe of Sadstoe, limestoe,.60 4 Triassi (Th) mudstoe, dolomite Group Reoubuo of Limestoe, dolomite Triassi (Tr) Group Jialigig of Limestoe, dolomite Triassi (T) Group Feixiagua Limestoe, dolomite,.74 4 of Triassi (Tf) mudstoe Permia (P) Limestoe, dolomite, mudstoe Carboiferous (C) Limestoe, shale.67 Siluria (S) Limestoe, mudstoe. 6 Ordoviia (O) Limestoe, shale, dolomite.0 6 Cambria( ) Limestoe, dolomite Siia (Z) Dolomite 3.34 M.Proterozoi (Pt) Geiss, migmatite, shist Upper-rust.9 6* Lower-rust.8 07* Togiag Zitog Chegdu Suiig Nahog Weiyua Chogqig Fig Isothermal map at depth 000m i Sihua Basi of Chia 05

4 Togiag Zitog Chegdu Suiig Nahog Weiyua Chogqig Fig Isothermal map at 4000m i Sihua Basi of Chia Togiag Zitog Chegdu Suiig Nahog Weiyua Chogqig Fig 3 Geothermal gradiet of sedimetal layer of Sihua Basi 06

5 Togiag Zitog Chegdu Suiig Nahog Weiyua Chogqig Fig. 4 eat flow distributio i Sihua Basi 07