Reservoir Characterization - Geocellular Model for Mandapeta sand of Mandapeta Field, KG Basin A Holistic Approach

Size: px

Start display at page:

Download "Reservoir Characterization - Geocellular Model for Mandapeta sand of Mandapeta Field, KG Basin A Holistic Approach"

Horatio Glenn
6 years ago
Views:

5th Conference & Exposition on Petroeum Geophysics, Hyderabad-2004, India PP 704-709 Reservoir Characterization - Geoceuar Mode for Mandapeta sand of Mandapeta Fied, KG Basin A Hoistic Approach V.K.Jain 1, P.

The main hydrocarbon bearing formation is Mandapeta sandstone of Lower Gondwana Group and has been assigned Permo-Triassic age.

1 5th Conference & Exposition on Petroeum Geophysics, Hyderabad-2004, India PP Reservoir Characterization - Geoceuar Mode for Mandapeta sand of Mandapeta Fied, KG Basin A Hoistic Approach V.K.Jain 1, P.K. Cherukupai 2, R.N.S.G.Rao 1, A.S. Bohra 1 & P.K. Tewari 1 1 Institute of Reservoir Studies, Ahmedabad, 2 Ex- ONGC ABSTRACT : Mandapeta fied is situated in the East Godavari sub-basin of Krishna-Godavari (K-G). The main hydrocarbon bearing formation is Mandapeta sandstone of Lower Gondwana Group and has been assigned Permo-Triassic age. The Mandapeta main pay sand (SAND-2) is the uppermost part of Mandapeta Sandstone and is gas bearing in wes A-01,03,05,06 07& 08. The paper deas with generation of fine scae 3D Geo-ceuar mode for Mandapeta SAND-2 in order to propery characterize the heterogeneity of the reservoir for the first time in any fied of K-G basin. This sand has been subdivided into five sub-units namey MDP-I, II, III, IV and V from bottom to top. The new structura stye interpreted from seismic, processed og parameters from ELANPLUS and reservoir data derived from we test have been used to buid Stratigraphic Framework Mode, We Mode and Attribute Mode, three basic constituents of the Geo-Ceuar Mode. The mode ceary demonstrates the variation in the reservoir properties and better ocaes for the expoitation of ocked hydrocarbon reserves. The areas in the up dip of A-01 in the cresta part and towards A-03 in the centra part of the fied may be chosen on priority for the expoitation of hydrocarbon. INTRODUCTION Vertica and horizonta variations in the properties of the reservoir (heterogeneity) have a significant impact upon fuid fow within a reservoir. Reservoir parameters such as porosity, water saturation and permeabiity derived from we og data define the vertica distribution of the properties at discrete positions in the fied. To capture the wide variations in the reservoir parameters it is necessary to map the attributes at a finer scae ateray as we as verticay. Geostatistics which takes contro from a the neighbouring we data provides a soution to these probems to some extent. The present new generation Geo-ceuar mode is abe to capture spatia variations in reservoir properties effectivey, which was not possibe earier. This has ed to the deveopment of a comprehensive reservoir mode needed for the interpretation and evauation of the interna reservoir architecture and distribution of reservoir properties for this fied. This has been attempted for the first time in any fied of K-G basin, which may further be extended to other fieds in this basin keeping in view the reservoir s compex ithoogy. MANDAPETA FIELD Mandapeta fied is ocated in the east Godavari subbasin (east of Gautami-Godavari river system) of K-G basin and is about 20 km SE of Rajahmundry town (fig-1). Figure 1: Location map of the Mandapeta fied. The fied was discovered in the year 1988 and attained importance because of Gondwana being new hydrocarbon exporation pay in Indian Basins, for the first time. Mandapeta sandstone and Goapai sandstone 704

Geoceuar Mode for Mandapeta sand of Mandapeta fied beonging to Gondwana group of sediments are the main hydrocarbon producers in this area (Fig:2). known as Sand-2 in the main bock.

2 Geoceuar Mode for Mandapeta sand of Mandapeta fied beonging to Gondwana group of sediments are the main hydrocarbon producers in this area (Fig:2). known as Sand-2 in the main bock.presenty gas is being produced from the fied mainy from one we and cumuative gas production as on is BCM. The other wes are not performing we and intermittent production is being taken from other two wes in the main bock. The main reason attributed for the discouraging resuts of production performance is due to poor reservoir properties of the formation (Manda et.a., 2001). Severa efforts put in the past coud not unock gas reserves and the probems remained unresoved. PETROPHYSICAL EVALUATION This Petrophysica anaysis has been carried out in the foowing phases: Figure 2 : Genera Stratigraphy of KG basin (after Venkatarangan et.a.) The we indicated presence of Paeozoic sediments comprising Coa-Shae-Sandstone sequence of Gondwana age, envisaging the subsurface extension of Pranhita-Godavari graben into this area. Foowing the discovery we, the area has been covered by 3D surveys (Banik, 95 & Singh, 2001) and ti date 23 wes have been dried so far. Commercia gas accumuation has been estabished in Mandapeta main bock (A ) where accumuation is within Mandapeta sandstone. In addition, Goapai Sandstone aso proved commercia gas accumuation in the southern part of the fied, which have been dried in separate faut bocks. Recenty a we dried in the east of the main bock has gone dry, imiting the extension of the pay sand in the bock. The main hydrocarbon bearing formation is Mandapeta sandstone of Gondwana Group and has been assigned Permo-Triassic age. Three pay sands are within this formation. The Mandapeta main paysand (Sand-2) is at the uppermost part of Mandapeta Sandstone, and is gas bearing in the main centra bock. Mandapeta Sand-1 is at a deeper eve, tested gas bearing on the western side of the fied. The Mandapeta main pay equivaent has been encountered as gas bearing in Mandapeta south area and named as Sand-2A. The present paper deas with the reservoir characterization of Mandapeta main paysand commony Log data of entire Mandapeta fied was processed & interpreted using in-house software ELAN PLUS with muti minera mode. Processed og presented as Parameter og depicting various reservoir parameters, e.g., porosity, water saturation, shae voume, permeabiity, etc. Cutoffs on porosity, Vcay and water saturation have been determined as 0.08, 0.35 and 0.8 respectivey. Layer-wise average reservoir parameters have aso been cacuated. Permeabiity vaues were taken from buid-up tests in wes A-01,03,05 and permeabiity was mapped throughout the fied (FER, ONGC). RESERVOIR PARAMETERS Reservoir parameters, water saturation, fushed zone water saturation, effective porosity, voume of shae, permeabiity, etc. have been computed at og samping rate for entire Mandapeta fied. These data have been oaded into OpenWorks database of Landmark workstation for making fine grid Geo-ceuar mode. The ayer wise average reservoir parameters for different Mandapeta pay units ike MDP-I, II, III, IV and V have been computed in each we of entire Mandapeta fied. GEOCELLULAR MODEL The main hydrocarbon bearing sand within the Gondwana Group of Mandapeta fied is the Mandapeta main pay sand (Sand-2), which is present through out the fied. It is heterogeneous, mutiayered sandstone castic reservoir 705

Geoceuar Mode for Mandapeta sand of Mandapeta fied interbedded by thin and tight shae/ sity shae bands deposited in the fuvia environment (Chary, 1988).

Figure 3 : N-S correation profie. Figure 5 : Sub-units of Mandapeta Sandstone (sand-2). are in the range of 10-16%. The sands appear to be more sity and cayey at paces.

In the area of study this sand has been subdivided into five sub-units, namey, MDP-I, II, III, IV and V from bottom to top (Fig.

3 Geoceuar Mode for Mandapeta sand of Mandapeta fied interbedded by thin and tight shae/ sity shae bands deposited in the fuvia environment (Chary, 1988). The thickness of this sand varies from 60 to 90 m consisting mainy of medium to coarse grained sandstone occasionay gritty, poory sorted interbedded with thin caystone and shae bands (Fig. 3 & 4). Figure 3 : N-S correation profie. Figure 5 : Sub-units of Mandapeta Sandstone (sand-2). are in the range of 10-16%. The sands appear to be more sity and cayey at paces. The mode ceary demonstrates the better reservoir facies distribution and its heterogeneities within the fied. Figure 4 : W-E correation profie. In the area of study this sand has been subdivided into five sub-units, namey, MDP-I, II, III, IV and V from bottom to top (Fig. 5) based on intervening shae/ caystone ayers, hard and tight, in paces, the thickness of these shae / caystone are very ess. The og motif corresponding to these subunits show the fining upward to bocky nature and occasionay coarsening upward with the buid up of resistivity at paces. The porosities The depth map on top of Mandapeta paysand derived from 3D seismic interpretation brings out the new structure stye (Fig. 6). The prominent E-W trending ow has been mapped in the main bock separating A-01 from A-03 & A-05, faing on other side of the ow. A NW-SE trending graben mapped on the east of the main bock of A appears to be devoid of hydrocarbon from the Mandapeta paysand (Sand-2) as substantiated by the dry wes (A-18 &23) faing in this corridor. The structura cosure brought out in the SW of A-06 is quite up dip and at much shaower eve. Better reservoir properties with higher pay thickness can be 706

It is quite cear from the depth map that A-01 which is under continuous production with better porosity and permeabiity is faing on the fank.

4 Imaging of Carbonate Terranes Appications to the Fort Worth Basin mode consists of ces equa to rows x. coumns x ayers and is shown at Fig.7. The number of fine ayers for individua sequence is as beow: Figure 6 : Structure Contour Map - Mandapeta Sand Top. anticipated in such areas. It is quite cear from the depth map that A-01 which is under continuous production with better porosity and permeabiity is faing on the fank. The we A- 03, ying on the other side of the ow, appears to be faing in unfavourabe structura position with poor reservoir characteristics in the main bock of the fied. Structure is rising further SW of A-03 and forms the favourabe ocae for the expoitation of HC. The southern bock of the main fied, the bock of A-08, mapped as downthrown faut cosure with GWC at m, ooks attractive in its up-dip areas with better reservoir attributes as depicted in the Geoceuar mode. The construction of Geo-ceuar mode consists of three stages, i.e., creating stratigraphic framework mode, defining we mode and buiding attribute mode. STRATIGRAPHIC FRAMEWORK MODEL Independent ayer MDP-I Bottom MDP-I bottom to MDP-I top 81 ayers MDP-I top to MDP-II bottom 4 ayers of SH-unit MDP-II bottom to MDP-II top 58 ayers MDP-II top to MDP-III bottom 4 ayers of SH unit MDP-III bottom to MDP-III top 66 ayers MDP-III top to MDP-IV bottom 5 ayers of SH -unit MDP-IV bottom to MDP-IV top 50 ayers MDP-IV top to MDP-V bottom 4 ayers of SH-unit MDP-V bottom to MDP-V top 54 ayers The first stage of creating framework mode required definition of surfaces to be used and the reationship of ayers to the overying and underying surfaces. The bottommost surface was taken as independent surface. This was done by importing the grid of bottom most surface from Z-map. The overying surface grids were then imported in stratigraphic succession. In the present study the surface grid of subunit MDP-I bottom was taken as independent surface and the framework was buit using the surface grid of other subunits top and bottom. The fine ayers (326+1=327) within the framework are considered as proportiona ayers. The thickness of the fine ayer is 30cm. The resuting framework WELL MODEL Figure 7 : Stratigraphic framework mode. In the we mode the attributes to be generated, viz., porosity, water saturation, Vshae and permeabiity, etc, defined in the form of ogs at we ocation, were read into the Starta Mode. The ces traversed by the we trajectory were assigned the properties. The present we mode is based on the data of 13 wes and the properties incuded are porosity, water saturation, Vshae and permeabiity. The porosity, 707

Geoceuar Mode for Mandapeta sand of Mandapeta fied Vshae and water saturation were the output from og data processing.

ones cut by the we trajectory were to be assigned vaues of the property being interpoated. These agorithms are geostatistica in nature.

The search radius contros the area extent over which the vaues are to be taken into consideration for assigning the weightages, and the power factor defines the weightages to the vaues.

5 Geoceuar Mode for Mandapeta sand of Mandapeta fied Vshae and water saturation were the output from og data processing. ATTRIBUTE MODEL After the framework mode and we mode were constructed, in the third stage buiding of attribute mode was carried out by defining the process (agorithm) by which the ces other than the ones cut by the we trajectory were to be assigned vaues of the property being interpoated. These agorithms are geostatistica in nature. In the StrataMode the ces are popuated using a method controed by parameters such as search radius and power factor. The search radius contros the area extent over which the vaues are to be taken into consideration for assigning the weightages, and the power factor defines the weightages to the vaues. In the present study a search radius of 4000 m and a power factor of 4 were used to buid the three dimensiona arrays of reservoir properties. The attributes of porosity, water saturation and permeabiity were generated. Figure 9 : Porosity distribution in N-S direction. Thus various attributes can be visuaized in various forms. The porosity, saturation and permeabiity distributions are presented in the form of cross sections (Fig.8, 9,10 &11). CONCLUSION Figure 8 : Sw distribution aong W-E direction. Fine scae Geo-ceuar mode is a very effective too for better reservoir characterization in any fied. It ceary defines the vertica and atera variations in the petrophysica Figure 10 : Porosity in A profie. properties of the reservoir in the given we and its spatia distribution in the entire fied can be generated through Attribute Mode. Five subdivisions of Sand-2 from bottom as MDP-I to V have been carried out and variation in their petrophysica properties has been defined. Favorabe areas for expoitation have been spotted out in the main bock based on the above study. The areas in the updip of A-01 in the cresta part and towards A-03 in the centra part may be taken up on priority. Better understanding of the fow units within the reservoir makes the job of deveopment geoogists easy, smooth and quick. 708

6 Geoceuar Mode for Mandapeta sand of Mandapeta fied REFERENCES Singh, Birba (2001), Integrated Interpretation of 3D seismic data, Mandapeta area, K-G basin, AP GEOPIC,ONGC. Manda, A.K; (2001), A Task force report on Expoitation of Mandapeta gas reserves,srbc Report Chary, G.S, (1988); We competion report of Mandapeta-01, unpubished report SRBC (ONGC): Formation evauation reports of a wes Banik, N.C; (1995), Interpretation of 3-D seismic data of Mandapeta area, ONGC report Venkatarangan, R, (1993), Litho-stratigraphy of K.G Basin Figure 11 : Permeabiity distribution in A profie. ACKNOWLEDGEMENTS Authors are gratefu to the management of ONGC for giving permission to pubish this work. Authors aso acknowedge ED-Head, IRS, ONGC, Ahmedabad, for providing an opportunity and a necessary faciities to prepare this paper. Sincere thanks are aso due to GM (wes), IRS,ONGC, for their critica comments during the progress of the work. Authors wish to acknowedge the support given by a coeagues in the group. 709

2.2.4 SOUTH VENTURE FIELD

Deveopment Pan Appication 249 2.2.4 SOUTH VENTURE FIELD 2.2.4. Fied History In 983, the discovery we South Venture O59 was dried to a tota depth of 66 metres. Mutipe, verticay stacked hydropressured and