TVN-01 TABLE OF CONTENT. Standard Disclaimer

Transcription

1 1 Company: NPN B.V Well: TVN-01 Prospect: Tiendeveen Country: Netherlands Analyst: Rana S. Amin Logging Date: Interval: m Report Date: RST Sigma Log Interpretation PRODUCT CODE: RST-SIGMA

2 TABLE OF CONTENT 1. Summary Introduction Objectives Main Results Log Quality Control and Processing Data Quality Data Processing Summary Appendices RST Tool Sketch Well Sketch RST-Sigma Standard Disclaimer The use of and reliance upon this recorded-data by the NPN (and any of its affiliates, partners, representatives, agents, consultants and employees)is subject to the terms and conditions agreed upon between Schlumberger and the NPN, including: (a) Restrictions on use of the recorded-data; (b) Disclaimers and waivers of warranties and representations regarding company's use and reliance upon the recorded-data; and (c)customer's full and sole responsibility for any inference drawn or decision made in connection with the use of this recorded-data. Page 2

3 1. Summary 1.1. Introduction The RST (Reservoir Saturation Tool) Sigma was run to determine the water saturation in the deviated (max 42 deg) well TVN-01 on 22 nd Dec The logging tool string was run on wireline and data recorded in real time. The logged interval which extends from m MDRT is completed with 3.5 liner (3.5 is 9.2 lb/ft weight, inner diameter & L-80 casing grade). This log was run in lieu of openhole logs as an obstruction at 3555m MDRT prevented the tools reaching TD. In order to maintain the integrity of the well the decision was taken to run casedhole logging tool (RST-Sigma), in order to characterise the reservoir objectives drilled in the hole. The logged interval was conducted over the tail of the well which is near vertical Objectives The main objectives were: Evaluate the Rotliegend and the Hardenberg sandstone water saturation for future well intervention. Evaluate thin sands between the base of the Hardenberg sandstone and TD Main Results The interpreted profile from the RST-Sigma data is presented in Fig-1. The interpreted profile indicates that hydrocarbons are present in both Rotliegend and Hardenberg reservoirs. The Hardenberg appears to be more water saturated compared to the Rotliegend. The thin sand units between the base of the Hardenberg (3638m MDRT) and TD also appear to be gas bearing. Page 3

4 Fig: 1- Interpreted profile of from RST-Sigma data. The profile shows that the Rotliegend and Hardenberg appear to be gas bearing. However, the water saturation in the Hardenberg is greater than in the Rotliegend. Page 4

5 Fig: 2- RST-Sigma composite profile. Page 5

6 2. Log Quality Control and Processing 2.1. Data Quality Log quality control was carried out on all logs. The logs were found to be of good quality. The repeat Sigma pass was in good agreement with the main log. All the borehole & casing parameters were put in place correctly Data Processing Summary The volume of shale (Vsh) was calculated from RST-SIGM & RST-GR and calibrated with the wellsite lithology. Effective porosity was calculated from TPHI (RST Sigma). Before determining the effective porosity, the data was calibrated with the data from offset well Geesbrug-1 (GSB-1). The porosity from the sonic data was compromised by poor compressional arrivals. For more detail refer to SSLT (Slim Sonic Logging Tool) interpretation report (dated 29 Dec 09). Due to the low porosity and uncertainty (due to low hydrogen index in gas-bearing zones the neutron porosity measurements such as RST porosity (TPHI) underestimate formation porosity) in porosity (Avg. 5%) in the Rotliegend the water saturation accuracy is likely to be +/- 30%. The water saturation error (+/- 10% -15%) in the Hardenberg is less than the Rotliegend as it has a greater average porosity (Avg. 10%). Water saturation from sigma was produced by using a formation water salinity of 200 ppk which was taken from the offset well GSB-1. Details about RST-Sigma are presented in Appendix 3.3. The drilling fluids will only impact RST data if there is invasion. In case of invasion, sigma can be affected; however it depends upon drilling fluids salinity/type and fluids in invaded zone. There is no indication of invasion from the logged data. Therefore, it is assumed that if there is any invasion, it is insignificant. The other following key parameters used for water saturation calculation (at borehole temperature 117 deg C & pressure 410 bar) are: Page 6

7 For Rotliegend Sigma Value c.u. (Capture Units) Water 96 Shale 54 Gas Matrix (Sandstone) 13 The sigma matrix value for the Rotliegend (13 captue units) is higher than the typical sigma matrix value (4-6 capture units, Appendix 3.3); this could be due to the high salinity of the formation water and salt plugging the pores. Sigma (Capture Units) Porosity (fraction) Fig: 3 Cross plot between Sigma (y-axis) & Porosity (x-axis) is indicating that with selected parameters all the data is in good agreement with each other. Page 7

8 For Hardenberg Sandstone Sigma Value c.u. (Capture Units) Water 96 Shale 54 Gas Matrix (Sandstone) 7.0 Sigma (Capture Units) Porosity (fraction) Fig: 4 Cross plot between Sigma (y-axis) & Porosity (x-axis) is indicating that with selected parameters all the data is in good agreement with each other. Page 8

9 3. Appendices 3.1 RST Tool Sketch Page 9

10 3.2 Well Sketch Tiendeveen proposed casing/completion scheme 2 Tubular Hole Casing/TOC/Formation, all depths from RT depth depth size Crown tubing hanger 11" x 3 1/2" AHRT TVRT m m WE-5 TR SC-SSSV OD 5.170", min. ID 2.812" /2" 13 3/8"shoe TOC 9 5/8" casing (channeled to 400m) KOP /4" 9 5/8" 43.5# Polseal N80 casing 3 1/2" 9.2# L80 tbg, collar OD 3.900", ID 2.992" TOC 7" /2" 9 5/8" casing shoe SPM w. dummy, OD 5.360", drift 2.867" WX LN max. OD 4.250", min. ID 2.750" RPBR max. OD 5.750", drift 2.867" Baker SB-3 prod. packer, min. ID 3.875" WXN NoGo LN max. OD 4.250", min. ID 2.640" WEG OD 4.250", min. ID 2.992" X-over 5" x 3 1/2", TOL 3288mAH " coupling OD 5.587", ID 4.276" 5" TOL: 3347 mah /8" MUST casing mAH 39m 7" 26# VAGT L80 casing, 7" shoe depth of 8 1/2" hole and 5" shoe /2" 9.2# 13%CrL80 VamAce liner, ID 2.992" 3 1/2" shoe Final depth Page 10

11 3.3 RST-Sigma Sigma Thermal neutron capture creates gamma rays and Sigma (macroscopic thermal neutron capture cross section) measurement is measuring the rate of this gamma ray population decay over time (Figure 3.3.1). Sigma mode records thermal neutron decay time distributions to provide capture cross-section data in a fast logging pass. The RST utilises dual neutron burst similar to TDT-P (Figure 3.3.2). It produces time decay distribution optimised for the determination of both borehole and formation sigma with low statistical variations. The count rate spectrum is recorded in 126 time gates of varying width, covering the entire sequence, including the burst and the "burst-off" background. Decay rates are corrected for pile-up losses and background and four apparent sigmas are computed, one for each burst/detector combination. Most environmental effects on nuclear measurements are too complex to be derived in practical analytical form. Instead tool response was characterized by acquiring a database of laboratory measurements in Schlumberger s Environmental Effects Calibration Facility (EECF) in Houston. The database was then parameterised in terms of the environmental variables that influence the measurement, such as: Formation porosity Lithology Borehole size Casing size Casing weight The characterisation was subsequently confirmed in the Europa test facility (located at that time in Aberdeen) for sigma and porosity and in the industry standard API porosity test pits for porosity alone. The four apparent sigmas are input to the database along with the environmental parameters and transformed to formation sigma (SIGM), porosity (TPHI) and borehole salinity (BSAL) by a dynamic parameterization and a classical weighted multiple linear regression. The output can be constrained by porosity or borehole salinity or both, but this is not normal practice (Figure 3.3.2). Page 11

12 Because chlorine has a large neutron cross capture section, sigma based saturation technique provides good results in areas with high formation water salinities. When the formation water is not sufficiently saline or when salinity is unknown, the sigma technique breaks down. Table-1 listed the typical sigma values for common formation matrix and fluids. Formation water saturation can be calculated using the equation illustrated in Figure 3.3.3, knowing the effective porosity, sigma values for formation matrix including shale/clay, volume of shale/clay, sigma values of formation fluids and measured sigma. In low formation water salinity, sigma water and oil are similar, thus it is impossible to distinguish water from oil. Therefore, saturation calculated from sigma measurement could have large error due to low contrast between oil sigma and water sigma. Figure Sigma Measurement Page 12

13 Figure Dual Neutron Burst and Sigma Measurement flow The same scenario for unknown water salinity or in mixed salinity due to water injection as the sigma saturation equation depends on known water sigma value. Carbon/Oxygen technique would provide better answer in these conditions as it is independent of salinity. Table-1. Typical Sigma Values Page 13

14 Figure Sigma Interpretation IRAT WINR RSCF RSCN Background corrected F/N inelastic ratio Weighted Inelastic ratio Far Detector Capture Count Rate Near Detector Capture Count Rate Page 14