Petroleum Engineering 324 Well Performance Daily Summary Sheet Spring 2009 Blasingame/Ilk. Date: Materials Covered in Class Today: Comment(s):

Transcription

1 Petroleum Engineering 324 Well Performance Daily Summary Sheet Spring 2009 Blasingame/Ilk Date: Materials Covered in Class Today: Comment(s):

2 Petroleum Engineering 324 (2009) Reservoir Performance Lecture: Orientation for Pressure Transient Testing: Objectives. Data (ALL data: reservoir, well, completion data, pressure/rate history). Analysis and Interpretation. Thomas A. Blasingame, Ph.D., P.E. Dilhan Ilk Department of Petroleum Engineering Department of Petroleum Engineering Texas A&M University Texas A&M University College Station, TX (USA) College Station, TX (USA) Slide /8

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4 Petroleum Engineering 324 (2009) Reservoir Performance Objective Provide orientation regarding the purpose, philosophy, and objectives for pressure transient testing. Thomas A. Blasingame, Ph.D., P.E. Dilhan Ilk Department of Petroleum Engineering Department of Petroleum Engineering Texas A&M University Texas A&M University College Station, TX (USA) College Station, TX (USA) Slide 3/8

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6 Orientation: PTA Purpose, Philosophy, Objectives Objectives of Pressure Transient Testing: Evaluate reservoir pressure (initial or average pressure). Evaluate reservoir fluid (fluid samples collected for lab study). Estimate reservoir properties (e.g., k, S, x f, λ, ω, etc.). Estimate reservoir volumetrics (e.g., fluid-in-place, drainage area). Input Data: BOTTOMHOLE pressure data (accurate to < part in 0,000 or more). SURFACE flowrate data (often poorly measured/recorded). Fluid properties (e.g., FVF, viscosity, compressibility,... ). Reservoir properties (e.g., h, φ, r w, c f,... ) Results of PTA Interpretation: Productive capacity of the WELL (damage/stimulation). Productive capacity of the RESERVOIR (transmissibility). Current average reservoir pressure. Reservoir limits (for production to pseudosteady-state). Well interference effects. Well/Reservoir specific parameters (e.g., C s, x f, λ, ω, L fault, r comp, k v /k h,...). Slide 5/8

7 Orientation: PTA Diagnostic Examples Unfractured Well Fractured Well p D, p Dd and p Dβd Type Curve Analysis SPE 2777 (Buildup Case) (Well in an Infinite-Acting Homogeneous Reservoir) Legend: Radial Flow Type Curve p D Solution p Dd Solution p Dβ d Solution p Dβd = Reservoir and Fluid Properties: r w = 0.29 ft, h = 07 ft, c t = psi -, φ = 0.25 (fraction) μ o = 2.5 cp, B o =.06 RB/STB Production Parameters: q ref = 74 STB/D Legend: p D Data p Dd Data p Dβd Data p Dd = /2 Match Results and Parameter Estimates: [p D /Δp] match = 0.08 psi -, C D e 2s = 0 0 (dim-less) [(t D /C D )/t] match = 5 hours -, k = 0.95 md C s = bbl/psi, s = 8.3 (dim-less) p D, p Dd and p Dβd Type Curve Analysis SPE 9975 Well 5 (Buildup Case) (Well with Infinite Conductivity Hydraulic Fractured ) Legend: Infinite Conductivity Fracture p D Solution p Dd Solution p Dβd Solution Legend: p D Data p Dd Data p Dβd Data p Dβd = /2 Reservoir and Fluid Properties: r w = 0.33 ft, h = 30 ft, c t = psi -, φ = 0.05 (fraction) μ gi = cp, B gi = RB/Mscf Production Parameters: q ref = 500 Mscf/D p Dd = /2 Match Results and Parameter Estimates: [p D /Δp] match = psi -, C Df = 0.0 (dim-less) [(t Dxf /C Df )/t] match = 0.5 hours -, k = md C fd = 000 (dim-less), x f = ft t D /C D t Dxf /C Dxf Field Example: (SPE 2777) Data match for a case of radial flow wellbore storage signature is identified using the pressure β-derivative. (dimensionless format p Dβd =) Field Example: (SPE 9975) Data match for the case of a well with an infinite conductivity vertical fracture formation linear flow behavior is revealed using the β-derivative. (dimensionless format p Dβd =/2) Slide 6/8

8 Orientation: Static Data for PTA PVT Properties: (Lab report preferred, correlations acceptable) Black Oil: B o, R s, μ o, c o (correlations require: T, γ g,sep, p b, γ STO ) Dry Gas: z (or B g ), μ g, c g (correlations require: T, γ g,sep ) Volatile Oil: Black oil equivalent or compositional formulation. Gas Condensate: Dry gas equivalent or compositional formulation. Water: B w, R sw, μ w, c w (correlations require: T, γ g,sep, p bw, salinity) Reservoir Properties: Porosity (φ) (core and/or well logs) Net pay thickness (h) (core and/or well logs) Wellbore radius (r w ) (well completion history (bit diameter)) Formation Compressibility (c f ) (c f =3x0-6 psia - or correlation) Well Completion History: Drilling records (initial pressures, production tests) Well files (well logs, core, PVT, recompletion, workover records) Annotated production records (records of activities very useful) Slide 7/8

9 Orientation: Production Histories Allocated Rate Data: Common in mature producing environments (e.g., Texas). Common in some offshore operations (manifold rates). "Allocation" depends on records and consistency checks. Poor/Incomplete (or Erroneous) Pressure Data: Virtually all production pressure measurements taken at surface. Completion changes often not reflected in surface pressures. Some pressure data are just wrong (poor gauge, poor timing, etc.). Well Completion Issues: Equipment changes, poor practices, failed equipment, etc. UNREPORTED activities (recompletions, workovers, treatments). Permanent DOWNHOLE Pressure Measurements: Expense is justified. Provides continuous evaluation of well performance. Data volume/sampling is an issue, but not a major problem. Slide 8/8

10 PTA Orientation: Tight Gas Production Case Example: Production History Plot East TX Gas Well Excellent rate and pressure histories. Unique case surface and bottomhole pressure data. MINIMUM data frequency for high resolution analysis point/day. Slide 9/8

11 PTA Orientation: Tight Gas Production Case Example: "Log-Log" Plot (Well Test Analysis) East TX Gas Well Used high frequency bottomhole pressure measurements (p ws ). Consistent match of surface and bottomhole pressure data. Outstanding example of "things done right." Slide 0/8

12 PTA Orientation: Early Well Deliverability From: Back-Pressure Data on Natural- Gas Wells and Their Application to Production Practices Rawlins and Schellhardt (USBM Monograph, 935). Well Deliverability: The first efforts to analyze well performance were an attempt to quantify well potential not to estimate reservoir properties. The original well deliverability relation was completely empirical (derived from observations), and is given as: 2 q = C( p - p2 ) n wf This relationship is rigorous for low pressure gas reservoirs, (n= for laminar flow). Slide /8

13 PTA Orientation: Well Deliverability Relation Darcy's Law: vr = qg Bg Ar = + k μ dp dr Separating and Integrating: qg r e p = e dr 2πkh r r p μg B w w g g Which Reduces to: [(μ g z) = constant] Performing the Pressure Integration: k dp [ Ar = 2πrh] or qg = (2πh) r μg Bg dr dp qg T z e w 2 πkh T psc ( μg z) c qg Bg p e p w Discussion: Derivation of Well Deliverability Relation Actually an empirical result (see Rawlins and Schellhardt (935)). Derivation from steady-state flow (above) is useful for illustration. Derivation for pseudosteady-state is similar (variety of results). psc p [ ln( r / r )] = sc sc p dp kh = 2π ln( re / rw ) Tsczsc T psc ( μg z) c ( p 2 e 2 T Tsc z zsc p 2 w) qg = C( p 2 e p 2 w) Slide 2/8

14 PTA Orientation: Well Deliverability (4-point test) From: Energy Resources and Conservation Board, 975, Theory and Practice of the Testing of Gas Wells, third edition, Pub. ERCB-75-34, ERCB, Calgary, Alberta. a. Typical flow regimes encountered during production (liquid system). b. Typical "flow-after-flow" or 4-point test, (assumes pseudosteady-state flow (each rate)). 2 ( p - p2 wf q = C ) c. "Deliverability" or "Backpressure" plot used to estimate maximum well productivity. Discussion: Well Deliverability (4-point test) Probably oldest "reservoir engineering" technique. Assumption of pseudosteady-state flow is the weakest link in analysis. Does not directly relate time, rate, and pressure performance. n Slide 3/8

15 PTA Orientation: Reservoir/Well/Facilities System Our focus is the reservoir... but, we also need to consider: The well completion. The tubulars. The surface facilities. The reservoir fluid(s). Overall flow system (after Fonesca). Blasingame axiom: "if there is a problem with the analysis/interpretation of well test and/or production data the issue most likely stems from the well completion." Slide 4/8

16 PTA Orientation: What Advances do We Need? Pressure Transient Analysis: PTA Data processing (permanent gauges) (obvious, but...). Numerical modelling (advise caution in applications). Variable-rate analysis (deconvolution). Better data analysis functions (We can always hope...). Continuous Measurement = Continuous Assessment Production Analysis: PA More consistent measurement of q and p wf. Pressure conversion (surface bottomhole). Further implementation of semi-analytical solutions. Diagnostic methods for defining pressure transient behavior in production data (model identification). Continuous Measurement = Productivity Optimization Slide 5/8

17 PTA Orientation: Questions to Consider Q. Practical applications of Pressure Transient Analysis (PTA)? A. Estimate/evaluate the following: Reservoir properties (e.g., k, S, x f, λ, ω, etc.). Productivity efficiency (damage or stimulation). Reservoir pressure (initial or average pressure). Q2. What are the major issues or complications in PTA? A2. Major issues/complications in PTA: (rarely volume) (direct assessment) (p avg long shut-in) Planning of pressure transient test. (always model prior to testing) Preparation of well for testing. (execution failures) Production history is not trivial. (can corrupt interpretation) Well completion have records at hand. (leaks, tubulars, placement) WHY YOU ARE TESTING THE WELL WHAT IS THE OBJECTIVE? Q3. Comparison with of PTA with Production Analysis (PA)? A3a. PTA (Pressure Transient Analysis) HIGH resolution/high frequency (pressure) data. (quality/quantity) Gives SNAPSHOT of the well performance at that time. (stress test) A3b. PA (Production Analysis) LOW resolution/low frequency (pressure) data. LUMPS entire life of well into analysis. (quality/quantity) (passive monitoring) Slide 6/8

18 Petroleum Engineering 324 (2009) Reservoir Performance Lecture: End of Presentation Orientation for Pressure Transient Testing: Objectives Data (ALL data: reservoir, well, completion data, pressure/rate history) Analysis and Interpretation Thomas A. Blasingame, Ph.D., P.E. Dilhan Ilk Department of Petroleum Engineering Department of Petroleum Engineering Texas A&M University Texas A&M University College Station, TX (USA) College Station, TX (USA) Slide 7/8

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20 Person on my left is: Person on my right is: Name: Petroleum Engineering 324 Well Performance Quiz 02 Derivative of a Logarithmic Function With Respect to Time [26 January 2009]. You are to solve the following problem related to the derivative of a logarithmic function with respect to time. Properties of the Natural Logarithm: Special Values: ln()=0, ln(exp(x))=x, ln( )= Integral Definition: Derivative Definition: Base Relation: x ln( x) = dx d [ x ] ln( ) = log( x ) = log0( x) = ln( x) x dx x ln(0) Given that p wf =p hr -m sl log(t), you are to derive the following expressions: a. The absolute value of the derivative of the wellbore pressure with respect to time: Ans. a: dp wf (Show all work) dt b. The "well testing" derivative (or "pressure derivative") function: Ans. b: dpwf Δ p' = t (Show all work) dt c. Comment on the behavior of the Δp' function: Aggie Code of Honor: An Aggie does not lie, cheat, or steal or tolerate those who do. Required Academic Integrity Statement: (Texas A&M University Policy on Academic Integrity) "On my honor, as an Aggie, I have neither given nor received unauthorized aid on this academic work." (your signature)

21 Person on my left is: Person on my right is: Name: Petroleum Engineering 324 Well Performance Quiz 02 Derivative of a Logarithmic Function With Respect to Time [26 January 2009]. You are to solve the following problem related to the derivative of a logarithmic function with respect to time. Properties of the Natural Logarithm: Special Values: ln()=0, ln(exp(x))=x, ln( )= Integral Definition: Derivative Definition: Base Relation: x ln( x) = dx d [ x ] ln( ) = log( x ) = log0( x) = ln( x) x dx x ln(0) Given that p wf =p hr -m sl log(t), you are to derive the following expressions: a. The absolute value of the derivative of the wellbore pressure with respect to time: dpwf d d m = [ p m log( t) ] = p sl hr sl hr ln( t) dt dt dt ln(0) dpwf d d m m d [ p ] sl = ln( t) 0 sl hr = [ ln( t) ] dt dt dt ln(0) ln(0) dt dpwf msl = dt ln(0) t dpwf msl = dt ln(0) t Ans. a: dp wf (Show all work) dt b. The "well testing" derivative (or "pressure derivative") function: Δ p' = dpwf m t t sl = dt ln(0) t Δp ' = dpwf m t = sl = constant dt ln(0) Ans. b: dpwf Δ p' = t (Show all work) dt c. Comment on the behavior of the Δp' function: Δp'=constant if p wf =p hr -m sl log(t) this behavior is definite and unique Aggie Code of Honor: An Aggie does not lie, cheat, or steal or tolerate those who do. Required Academic Integrity Statement: (Texas A&M University Policy on Academic Integrity) "On my honor, as an Aggie, I have neither given nor received unauthorized aid on this academic work." (your signature)