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Logs : how to use them for QUALITIATIVE reservoir evaluation

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Presentation on theme: "Logs : how to use them for QUALITIATIVE reservoir evaluation"— Presentation transcript:

1 Logs : how to use them for QUALITIATIVE reservoir evaluation

2 Program : how to use logs for qualitative reservoir evaluation
- Introduction/Objective Drilling/Mudlogging – A brief overview Depth and Datum reference Drilling/Mudlogging. Mandatory data for logs interpretation Logging Tools/Data acquisition Tools – Principles (Brief or Optional) Data acquisition – Quality Control Quick-look Methodology – « Understand » the well Main steps of the Quick Look approach Example #1: Sand/Shale environment  Correction with Quantitative results Example#2 : Carbonates environment  Correction with Quantitative results Conclusion/Main points MGU – 20th Mar. 2014

3 Different types of rigs…
…always the same measurements

4 Why logging acquisition (LWD or WL)
Geological aspect: Sedimentology Structural Links with Geophysic (seismic) Time Depth conversion Petro elastic Model Reservoir aspect  Main subject of this 1 day course Net to Gross Porosity Saturation MGU – 20th Mar. 2014

5 GEOLOGICAL ASPECT Large scale interpretation (decametric to hectometric) Logs = a continuous outcrop of several thousand meters thickness Logs for Explorationists – Pau– 10 – 14 June 2013

6 WELL vs seismic relationship
Well to seismic Tie Petro Elastic Model Reservoir Characterization Fluid characterization Fluid Substitution Monitoring (4D) Logs for Explorationists – Pau– 10 – 14 June 2013

7 Wire Line depth is the reference
References Depth/Datum MD : Measure Depth/RT TVD : True Vertical Depth / RT TVDSS : True Vertical Depth / MSL (Mean Sea Level) For all of them (MD, TVD,…) « Driller » and « Logger » depth are available Wire Line depth is the reference MGU – 20th Mar. 2014

8 Gas shows 2/2 MGU – 20th Mar. 2014

9 Vertical resolution (cm)
DEPTH OF INVESTIGATION vs VERTICAL RESOLUTION FLUSHED ZONE Vertical resolution (cm) L’amélioration de la résolution verticale des outils de résistivité profonde se fait en général au détriment de la profondeur d’investigation. Noter la bonne performance de la famille des «array inductions», qui provient d’un processing conbinant la bonne résolution des mesures proches et la lecture profonde de très mauvaise résolution verticale. Les outils radio-actifs sont handicapés par le temps d’intégration (comptage des particules) et pour certains l’espacement entre les émetteurs/récepteurs. NMR Depth of investigation (cm) - MGU – 20th Mar. 2014

Unflushed Zone Flushed Zone Rt Rw Rxo Rmc Sw Rmf Mud cake Rm Rt Sxo Rs Resistivity Par la force des choses, les outils de mesure sont situés dans le trou de forage. Entre l’outil et la formation que l’on désire mesurer se trouvent la boue, le mud-cake et, pour les outils de résistivité profonde la zone envahie par le filtrat de boue. Ces effets indésirables se traduisent: - dans le pire des cas, par la perte des données, - sinon, par la nécessité de corriger d’effets d’environnement, - ou bien de corriger d’invasion. Il faudra également prendre en compte le fait que les zones d’investigation des différents outils peuvent être différentes. Rxo Shoulders Rmc Rayon Rm Drilling Mud Borehole axis - MGU – 20th Mar. 2014

Raw data Logs QC and badhole detection Non Reservoir levels identification Shaly levels tight levels Reservoirs intervals Lithology Determination  Logs and Xplot Shaly reservoir Clean reservoir Hydrocarbon Bearing reservoir Gas effect identification Water bearing reservoir NEW 2009 – Anthony Price Porosity determination Rw (SP, Archie…) Sw (Archie Formula) MGU – 20th Mar. 2014

Net Reservoir and Net Pay definitions SWT Gross reservoir Net Reservoir Net Pay Top Waste Zone Top réservoir HCWC Base réservoir MGU – 20th Mar. 2014

13 + LITHOLOGY DETERMINATION Neutron/Density (limestone calibration)
Identification of lithology in the water zone Neut/Dens separation around 6 p.u.value  Pure Sandstone response Limestone compatible scale Water bearing zone + Shale #6 pu Sandstone Water bearing PEF Quartz value : 1.8/2 B/E Limestone Water bearing Dolomite Water bearing #14 pu Shale PEF (Photo Electric Factor) Good consistency between all the is mandatory Neut/Dens separation around 10/14 p.u.  Pure Dolomite response NEW 2009 – Anthony Price PEF is independant of the porosity. PEF Dolomite value : 3 B/E PEF Limestone value : 5 B/E Neut/Dens superimposed  Pure calcite response

Comparison between Rhob and Nphi Oil : extremely limited impact (Rhob and Nphi mainly impacted by lithology) Gas : effect superimposed on lithology effect Rhob value decrease  Phi_Dens overestimated due to the very low density of gas Nphi value decrease  Phi_Neutron underestimated due to the very low IH of gas Neut/Dens Separation increase when Gas saturation is high close to the borehole. If this zone is partially or completely flushed by the mudfiltrate, the Gas Effect is reduced or null If the porosity is very low (tight gas) Gas effect can be very low or null Gas and Oil can not be differentiated with resistivity Gas effect in Limestone Reservoir Gas effect in Sandstone Reservoir NEW 2009 – Anthony Price Gas Gas Water MGU – 20th Mar. 2014

From Quick Look Method From Quantitative interpretation Porosity in the water or oil zone  Direct value on Neut/Dens Porosity of the reservoir with gas effect (known lithology)  Direct value on Neut/Dens Limestone calibrated 0.00 Water Sst: Porosity 15% Water Lst: Porosity 15% Water Dolomite: Porosity 15% Half of the Neut/Density Separation 0.00 Gas Sst: Porosity 16.5% 1/3 2/3 1/3 – 2/3 of the Neut/Density Separation MGU – 20th Mar. 2014

16 Contacts determination
From Quick Look Method From Quantitative interpretation Comparison Rxo et Rt In the water leg: Low Resistivities Rt // to Rxo over a significant thickness. Contact Water – HC  Rxo translated on Rt Gas – Oil Contact Oil – Wat Contact HC – Wat Contact Low Res + curves // MGU – 20th Mar. 2014

Archie Formula for clean reservoir only S a R w m t n = æ è ö ø × F In a water bearing reservoir : Sw = 1  - Common value for a :1 Common value for m :2 F determined by quick look Rt measured by resistivity tools (Deep Investigation) Rw = Fm x Rt a Rw can be calculated in the water zone Sw in the hydrocarbon bearing zone. Can be calculated on several points during a quick look approach NEW 2009 – Anthony Price Porosity estimation in the water zone  Rw Determination Sw = 100% Rt : Red curve

Take into account all the mudlogging (gas, cuttings…) and drilling data (drilling phase, mud properties…) Logs Quality Control is a mandatory step before any type of interpretation Impact of a deep mud filtrate invasion Impact of borehole shape (washout, mudcakes) Detect any kind of acquisition problem Consistency between tool answers is very important. If not questions have to be asked: Problem of mineralogy Problem of fluids Problem of acquisition Be careful with resistivity variations: a lot of informations within these curves but affected by many parameters: Fluid content (Water, mud filtrate, HC) Porosity Water salinity Cementation factor « m » Each interpretation – Quick Look or quantitative – has to be geologicaly coherent. It means volume of minerals and porosity have to be compatible with the regional context MGU – 20th Mar. 2014

Rhob Nphi DT PEF GR g/cc v/v us/ft B/e API Quartz 2.65 -0.02 55 1.8 Low Calcite 2.71 49 5 Dolomite 2.86 0.02 44 3 Anhydrite 2.96 -0.01 50 Salt 2.16 67 4.65 Pyrite 39 17 KFeldspar 2.52 69 High Micas (muscovite) 2.82 0.2 2.4 Barite 4.48 267 Lignite 1.19 0.47 160 Be careful with resistivity variations: a lot of informations within these curves but affected by many parameters: Fluid content (Water, mud filtrate, HC) Water salinity Cementation factor « m » linked to tortuosity of the porous network 1.6/1.7 in unconsolidated reservoir (very high porosity and permeability) Around 2 in “classical” clastic reservoir Up to 2.3/2.5 in tight or very tight clastic reservoir Extremely variable in carbonates reservoir Porosity NEW 2009 – Anthony Price MGU – 20th Mar. 2014

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