PETROLEUM DEVELOPMENT GEOLOGY RESERVES ESTIMATE

• The most important role of a DG is to: – estimate the oil and gas reserves that may be discovered in a particular venture – keep track of the reserves in all past ventures Educated Guess and/or Comparison with nearby production Static Reserves Estimates Ü Volumetric Calculations Dynamic Reserves Estimates Ü Ü Ü Decline Curve Analysis Material balance calculations Reservoir Simulation • Consider a region where production is from a highly fractured tight formation or where poroperm heterogeneity is unpredictable • Volumetric calculations are largely meaningless • A way to estimate potential production from a well is to consider those nearby • Generally, such a wildcat well will not perform better than the nearest wells: best to estimate cautiously • Most accurate and widely used methods of reserves estimation • Carried out by geologists as they are based on geological structure and isopach maps • Rock volumes are established that are assumed to contain hydrocarbons (e.g seismic bright spot) • Can be a simple volume calculation or a complex net gas or net oil isopach approach, determined by structure contours modified by fluid contacts and net isopachs (net reservoir thickness map) • Accuracy of volumetrics depends on data for porosity, saturation, net thickness, areal extent, formation volume factor, integrity of those data within a reservoir Volumetric Method • RR = 7758 x A.t x φ(1 – Sw) x FVF x RF • Amount of oil in reservoir ̇ RR ̇ 7758 = = ̇ ̇ ̇ ̇ ̇ = = = = = A t φ (1-Sw) FVF ̇ Bo/Bg ̇ RF • Amount of recoverable oil Recoverable Reserves conversion from acreft to barrels (if vol in m3 this conversion number is eliminated) area of porous rock, acre thickness in feet porosity,% water saturation of reservoir Formation Volume Factor (1/Bo & 1/Bg) å reservoir volume / surface volume (vr / vs ) = Recovery Factor • Most rock volumes established through use of net gas and net oil isopachs (net pay map) • Constructed from superimposing of net isopach map and structure contour maps then cut (reduced) it with well defined OWC and/or GOC • Calculate the volume of net pay map by planimeter (or digitizer table) and/or grid square counting HORIZON MAP (Superimposed Structure and Net Isopach Maps) 0m 5m 10 m 15 m 10 m 5m 0m NET PAY MAP Example Exponential decline Rate, stb/d 10000 q = 6049.1e -0.0524 t 1000 Slope=-D 1/quarter year 100 10 20 30 40 time (quarter year) 50 60 Example Rate decline with production 7000 6000 q = -0.4301Np + 5768.7 q stb/d 5000 4000 Reserves 3000 2000 q abondonment 1000 0 2000 4000 6000 8000 10000 Cum prod, MSTB 12000 14000 12000 40 Rate (stb/d) 30 8000 25 6000 20 15 4000 10 2000 0 Time (years) 10 12 14 16 Cum Production (MMstb) 35 10000 Hyperbolic Decline curve 10000 9000 8000 q STB/D 7000 6000 5000 4000 3000 2000 1000 0 50 100 150 200 days 250 300 350 MATERIAL BALANCE of a Petroleum Reservoir (Mostly carried out by Reservoir Engineer) General Concept of Material Balance a Initial reservoir conditions From: Petroleum Reservoir Engineering — Amyx, Bass, and Whiting (1960) b Conditions after producing Np STB of oil, and Gp SCF of gas, and Wp STB of water Material Balance: Key Issues ̈ ̈ ̈ ̈ Must have accurate production measurements (oil, water, gas) Estimates of average reservoir pressure (from pressure tests) Suites of PVT data (oil, gas, water) Reservoir properties: saturations, formation compressibility, etc RESERVOIR SIMULATION (RS) • Reservoir Modelling: primarily the reservoir engineer’s job • RS applies the concepts and techniques of mathematical modeling to the analysis of the behavior of petroleum reservoir systems • In a narrower sense å refers only to the hydrodinamics of flow within reservoir • In a larger sense å refer to the total petroleum system which includes the reservoir, the surface facilities, and any interrelated significant activity, and economic • The basic flow model å the partial differential equations using finite difference methods which govern the unsteady state flow of all fluid phases in the reservoir medium INPUT PROCESSED in the BLACK BOX OUTPUT Rock data Reserves Fluid data Production data Reservoir model Pressure data Plan of reservoir depletion Flow rate data Mechanical & operational data Miscellaneous data RESERVOIR SIMULATOR Production forecast Optimum production Reservoir link with surface facility The Role of DG in Reservoir Simulation • Prepare the array input data (maps) of individual flow unit : structure (top & bottom), isopach (net & gross), porosity, permeability, rock compressibility etc • Advising to simulation engineer in the designing of the grid model and layer divisions • Trace and established in the model grid the existence of faults, horizontal and vertical barriers permeability • During the history matching of production, pressure etc., DG advises to simulation engineer in allowable geological modification such as thickness, structure, rock properties and volumetric reserves • PROVED : – Estimated to reasonable certainty Often based on well logs but normally requires actual production or formation tests – Proved developed reserves – Reserves that are expected to be recovered from existing wells – Proved undeveloped reserves – To be recovered by new drilling, deepening wells to a new reservoir or where additional finance is required to produce • PROBABLE RESERVES – Less certain than proved but can be assessed to some degree of certainty May include logging estimates, improved recovery technique estimates • POSSIBLE RESERVES – Not as certain as probable reserves and can only be estimated to a low degree of confidence • UNPROVED RESERVES å Resources Decision Making: protocol • Despite these defined terms, there is still some latitude in their application In general, we use this: • Proved Reserves = minimum case economics Financial investment is based on proved reserves • Proved + Probable Reserves = most likely case economics Internal company decisions usually based on this • Proved +Probable + Possible Reserves = maximum case economics This is the best that could reasonably happen for a venture Companies try to sell ventures based on this MM DARISSALAM, YOGYAKARTA JUN ‘08 [...]... of certainty May include logging estimates, improved recovery technique estimates • POSSIBLE RESERVES – Not as certain as probable reserves and can only be estimated to a low degree of confidence • UNPROVED RESERVES å Resources Decision Making: protocol • Despite these defined terms, there is still some latitude in their application In general, we use this: • Proved Reserves = minimum case economics... volumetric reserves • PROVED : – Estimated to reasonable certainty Often based on well logs but normally requires actual production or formation tests – Proved developed reserves – Reserves that are expected to be recovered from existing wells – Proved undeveloped reserves – To be recovered by new drilling, deepening wells to a new reservoir or where additional finance is required to produce • PROBABLE RESERVES. .. rate of production is graphed – Generally 6 months – 1 year after start of production • Good reserves estimates can be derived Often compared with volumetric technique results • Can be done by well, by a group of well, by block, by reservoir, by field Decline Analysis Results • Determine remaining recoverable reserves under natural depletion rate • To forecast production under existing conditions • Limitation:... in their application In general, we use this: • Proved Reserves = minimum case economics Financial investment is based on proved reserves • Proved + Probable Reserves = most likely case economics Internal company decisions usually based on this • Proved +Probable + Possible Reserves = maximum case economics This is the best that could reasonably happen for a venture Companies try to sell ventures based... q stb/d 5000 4000 Reserves 3000 2000 q abondonment 1000 0 0 2000 4000 6000 8000 10000 Cum prod, MSTB 12000 14000 12000 40 Rate (stb/d) 30 8000 25 6000 20 15 4000 10 2000 5 0 0 0 2 4 6 8 Time (years) 10 12 14 16 Cum Production (MMstb) 35 10000 Hyperbolic Decline curve 10000 9000 8000 q STB/D 7000 6000 5000 4000 3000 2000 1000 0 0 50 100 150 200 days 250 300 350 MATERIAL BALANCE of a Petroleum Reservoir... Engineer) General Concept of Material Balance a Initial reservoir conditions From: Petroleum Reservoir Engineering — Amyx, Bass, and Whiting (1960) b Conditions after producing Np STB of oil, and Gp SCF of gas, and Wp STB of water Material Balance: Key Issues ̈ ̈ ̈ ̈ Must have accurate production measurements (oil, water, gas) Estimates of average reservoir pressure (from pressure tests) Suites of PVT data... reservoir engineer’s job • RS applies the concepts and techniques of mathematical modeling to the analysis of the behavior of petroleum reservoir systems • In a narrower sense å refers only to the hydrodinamics of flow within reservoir • In a larger sense å refer to the total petroleum system which includes the reservoir, the surface facilities, and any interrelated significant activity, and economic... å the partial differential equations using finite difference methods which govern the unsteady state flow of all fluid phases in the reservoir medium INPUT PROCESSED in the BLACK BOX OUTPUT Rock data Reserves Fluid data Production data Reservoir model Pressure data Plan of reservoir depletion Flow rate data Mechanical & operational data Miscellaneous data RESERVOIR SIMULATOR Production forecast Optimum ... logging estimates, improved recovery technique estimates • POSSIBLE RESERVES – Not as certain as probable reserves and can only be estimated to a low degree of confidence • UNPROVED RESERVES. .. volumetric reserves • PROVED : – Estimated to reasonable certainty Often based on well logs but normally requires actual production or formation tests – Proved developed reserves – Reserves that... 1 Educated Guess and/or Comparison with nearby production Static Reserves Estimates Ü Volumetric Calculations Dynamic Reserves Estimates Ü Ü Ü Decline Curve Analysis Material balance calculations