Produced Water Reinjection Performance Joint Industry Project TerraTek, Inc. Triangle Engineering Taurus Reservoir Solutions (DE&S) E-first Technologies Advantek International

Completion skin in various types of completions in PWRI (in soft sands and in general) A.(Tony) Settari, D.A. Walters TAURUS Reservoir Solutions Ltd.

Motivation: All soft sands data sets (except fractured chalk) show large reduction in observed injectivity compared to theoretical It is necessary to identify which part of the completion is the bottleneck and conpare options (part of best practices for Task 3) Deliverable: method for estimating completion skin for calculation of overall II for several different types of completions

Completions considered – vertical well 1)Open hole (baseline) 2)Screens and slotted liners 3)Cased and perforated 4)Fracpack Some general, some specific to soft formations

Open hole II (baseline) S OH – open hole mechanical (drilling) skin D – non-Darcy skin  P = q L  L B L [ln(r e /r w ) + S OH + D q L ] /(k R h R ) II = q L /  P

OH Completions with Screens –Screen skin S s generally considered negligible for clean screens –Measurements by Asadi & Penny (2000) at relatively low rates (6-18 BPD/ft) –2040 PMF, 2040 Stratapack, prepacked wire wrap with 4060 RC sand –Extrapolation to higher rates using assumption  p =C V 2

Extrapolated data for dp through clean screens

Effect of solids on screens  Catastrophic decrease in permeability  Cleanup operations restore only 10 % of original permeability (recovery factor F R < 0.1  Total skin S = S OH + S S F R

Slotted liners n Liner skin called “slot factor” n Skin is a function of slot density (or open area) and slot width n Skin on the order of 1-10 possible n Additional effect of blank sections

Slot skin for clean liner (Kaiser et al., 2000) S = S OH + S L

C+P completions  Loss is expressed via Injectivity Ratio (IR) compared to OH, undamaged completion  Can be expressed by equivalent skin:  p = pressure drop in a near-well region to radius r b q = injection rate S = ln(r e /r w ) (1- IR)/IR

Components of perforation losses 1)Geometry of perf pattern (I.e, effect of perf tunnel dimensions, spf and phasing) for clean perfs 2)Collapse of perf tunnel (due to dilation and softening of material …) 3)Fill-up of perf tunnels with gravel, solids, produced sand from upsets, etc. 4)Turbulence at high injection rates

Method of evaluation Specialized near-well reservoir simulator, single phase (PERF3D) Models each individual perf inside the overall cylindrical geometry Any spacing and phasing Perf tunnel can be empty or filled Laminar flow or turbulence

Geometry of the model

Case I : Geometry effect n Empty perforation of decreasing L p, laminar flow n Limit to L p =0 modeled by filled perf with same properties as reservoir (k, phi) n Results expressed as IR (injectivity ratio) IR = II perforated / II openhole n Results are INDEPENDENT of permeability

2 spf, dp=0.5 inch

4 spf, dp=0.5 inch

Case II : Filled perforation n Laminar flow n Filled perf with same phi as reservoir, k p = k res x factor n Results again INDEPENDENT of permeability

2 spf, dp=0.5 inch, filled perfs

2 spf, dp=0.5 inch, empty perf, turbulence effect (underestimated)

Method of evaluation n Choose intact, collapsed or gravel packed perf geometry n Generate appropriate charts for the basic skin IR p (these are independent of permeability) n Generate chart for the effect of turbulence, multiplier F T n Total IR = IR p F T, convert to S p

Example of application Pay height100 ft Permeability1600 md Porosity 25 % Reservoir Temperature 170 °F Injection Temperature 80 °F Reservoir pressure2500 psia Initial minimum stress 3500 psia Water FVF1.03 Water viscosity0.4 cP Drainage radius1750 ft Wellbore radius ft Initial (openhole) skin 20 Perforating pattern: 4 spf, 90 deg phasing, 0.4 inch diameter, 6 inch length Pay height100 ft Permeability1600 md Porosity 25 % Reservoir Temperature 170 °F Injection Temperature 80 °F Reservoir pressure2500 psia Initial minimum stress 3500 psia Water FVF1.03 Water viscosity0.4 cP Drainage radius1750 ft Wellbore radius ft Initial (openhole) skin 20 Perforating pattern: 4 spf, 90 deg phasing, 0.4 inch diameter, 6 inch length Assume max inj dp = 1000 psia, calculate OH, Screen, C+P injectivities for matrix injection

Results

Conclusions  The openhole, undamaged calculation gives very large, unrealistic values  There may be a significant pressure drop across screens at high rates. Lab or field data at representative rates is necessary to confirm this.  Perforation skin can be high if the perfs are filled, and can account for a large portion of the observed total skin in the field.  There is a large variation in predicted injectivity (333,000 – 12,000 bpd) depending on the completion configuration and assumptions used.

Conclusions (continued)  The methodology can be used to estimate and compare possible skins from different types of completions  Possibility to extend the work to develop a comprehensive tool (requires a series of simulations with PERF3D to parameterize perforation skins)