petrophysical review of 10 well...

Petrophysical Review Of 10 Well Project

Introduction

This report represents the results of the evaluation of log (aided bycore analysis data when available) over Triassic, Zechstein andCarboniferous formations for 10 wells in the Southern North Sea.

Intervals of interest:

• Triassic Middle Bunter Sandstone formation.

• Zechstein Haupdolomite formation

• Carboniferous Yoredale & Scremerston formation

Wells Analysed

Well Drilled Status

42/13-1 1968 P&A

42/12-1 2010 P&A

42/14-1 1970 P&A

42/15a-2 1990 P&A (Gas)

42/15b-1 1984 P&A (Gas)

43/11-1 1973 P&A

43/6-1 1997 P&A

43/13a-5 2008 P&A

43/8-1 1970 P&A (Gas)

43/8-2 1970 P&A

Objectives

A key objective has been to adopt a consistent methodology to theinterpretation of the log data such that regionally compatible results arecreated. The methods used in this study are industry standard techniquesthat are widely used in the evaluation of reservoir properties in the typesof formations encountered in this area of the Southern North Sea.

• To create a complete and standardised dataset from the many vintagesof data.

• To produce a petrophysical evaluation of the reservoir quality throughthe integration of wireline logs, and available core and fluid analysis.

Pre-Processing Phase

• Data provided by the client has already put through theminimum pre-processing procedures

• All the data provided came from I H S (and CGG). Thesedatasets came in a composited format, environmentallycorrected, on-depth and edited out for casing & firstreading effect

Evaluation Phase

This has been done in the following manner:

1. By Lithological (tops)/Petrophysical Sub Zonation.

2. Clay Volume determination

3. Porosity Evaluation

4. Water Saturation Analysis

5. Net thickness & Summation of Reservoir properties

6. Reporting

Lithological/Petrophysical Zonation

• Zonations within Stratigraphicalunits based on log characteristics.

• These reflect changes in rockmatrix and/or clay properties

• Identified from log plots &crossplots with reference togeological data

Reservoir zoned to reflect changes rock typeWell 42/14-2

1. Clay Volume Determination

• Gamma ray & Crossplot & Histograms techniques

• Consisted methologyapplied throughout different formations

• Shale technique to suit different lithologies.

D-N crossplot to identify clean and

shale points.

Histogram is created to obtain 5-95

percentiles which represent Clean and

shale ends.

2. Porosity Evaluation

• Assesment of Effective Porosity

• Correction for Clay & Hydrocarbon

• Calibration against Core Data

• Single log & CrossplotTechniques Applied

Core data, D-N crossplot and CPI from 42/15a-2

3. Water Saturation Analysis

• Clean and Shaly models applied: Archie was used for clean intervals and Simandoux for shaly sections.

• Consistent application of models within each stratigraphical unit

• Regional assessment of formation water salinities from water analysis & log data

This data comes from 42/15a-2

Rw obtained from Pickett plot aboveand Rt from log.

4. Net Thickness – Reservoir Summations

• Volume of clay, porosity & water saturation cut offs defined per reservoir.

• Consistent application through all wells

• Net pay zones highlighted on CPI plots

• Zone averages tabulated by well and reservoir unit

• Net thickness, Net/Gross, Average Porosity & Water saturation.

This summation was taken from well 42/15a-2

Zones Z1 Z2 MBSS

Depths (MD) 1386 -1402.6 m1402.6-1411.37

m 1411.37-1502.5 m

Depths (TVDSS)1346.4 -1362.6

m1362.6 1371.34

m1371.34 - 1462.59

m

Gross 16.752 8.92 91.28

Net 5.944 1.28 85.65

N/G 0.355 0.144 0.938

Avg Porosity (RES) 23.20% 15.50% 18.10%

Avg Water saturation (RES) 6.70% 100% 90.60%

Cut offs PHIE > 0.08

VCLAY < 0.5

SW < 0.6

Example 1 From Middle Bunter Sandstone Reservoir

Well 43/8-1 p&a Gas discovery. Dst measured flows of 17 mmcf/d & 31 mmcf/d in zone 1 middle bunter

sandstone fm.

Zones Z1 Z2

Depths (MD) 5699' -5868' 5868' - 5976'

Depths (TVDSS) 5613 - 5782' 5782' - 5890'

Gross 169.5 108.5

Net 104.25 27.75

N/G 0.615 0.256

Avg Water saturation (res)

30.6 100%

Avg Porosity (res) 13.90% 10.60%

Avg Porosity (pay) 15.70% 0

Avg Water saturation (pay)

30.6 0

Avg Volume of Shale (pay) 7% 0

Porosity SW Vclay

ZONE method equation clean-clay method

1 D-N Archie 47-128 Linear GR method

2 D-N Archie 55-109 Linear GR method

Rw is around 0.02 ohm m @ Reservoir temperature of 150 F. This value

correspond to this formation in SNSE

Evaluation methods

for this well and above net

thicknesses and reservoir

parameters

Example 2 From Carboniferous Reservoir

Well 42/15a-2. p&a gas well.Reservoir Carboniferous yoredale formation

Porosity SW Vclay

ZONE method equation clean-clay method

1 D-N Simandoux 27-81Linear option

using CGR


using CGR


using CGR

4 D-N Simandoux 6.2-118Neutron Density

xplot

5 D-N Simandoux 22-68Neutron Density

xplot


using CGR


using CGR

Zones Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7

Depths (MD) 2381-2386 m2386-

2419.48 m2419.48-

2431.76m2431.76-2531.87

m2531.87-2543.35

m2543.35-

2578.54 m2578.54-

2651.41 m

Depths (TVDSS)2351.61-2356.6 m

2356.6-2390.06 m

2390.06-2402.33 m

2402.33-2502.37 m

2502.37-2513.84 m

2513.84-2459.01 m

2549.01-2621.81 m

Gross 4.997 33.458 12.272 100.04 11.471 35.161 72.807

Net 3.876 0.609 8.072 2.105 10.029 3.51 45.89

N/G 0.776 0.018 0.658 0.021 0.874 0.1 0.63

Avg Porosity (RES) 11.50% 9.30% 13.70% 11.90% 10.30% 8.10% 11.20%

Avg Water saturation (RES) 45.90% 100.00% 37.90% 60% 91% 94.20% 91.60%

Avg porosity (pay) 12.20% 0 14.90% 14.30% 0 0 0

Avg Water saturation (PAY) 42.20% 100% 37.90% 42.40% 100% 100% 100%

Histogram shows 5-95 percentiles which represent clean and shale range. On the right, there is

evaluation methods used.

Pickett plot determines Rw & m and confirmlocal values

This reservoir had to be zoned in 7 sections and thicknesses and reservoir parameters shown

Deliverables

• CPI of formation of interest

• Images of Crossplots of D/N, D/S, Picket plots, histograms….

• LAS file with all curves plus analysis curves, PHIE, SW, VCLAY, BVW, Mineral volumes….

• Logging parameters. A spreadsheet with relevant information

• Summation report. It contains all net thicknesses, N/G, Averages…

• Written report. This document explains methodology, equations used, run information and observation.

petrophysical review of 10 well...

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