Basics of peroleum engineering
- 1. Basics of Peroleum Engineering
- 2. Permeability is a property of a porous medium that characterizes the ease with which fluids flow though it. PERMEABILITY • Intrinsic property of the medium • Along with the porosity, it tells how fit the formation is to be classified as a potential reservoir • S.I. Unit: m2 (square metre) • Common unit: darcy ( or milli darcy) • By knowing the conductivity, permeability can be calculated by the Darcy’s law. Factors affecting permeability: • Porosity • Stacking of the individual grains (packing) • Sorting • Sphericity and roundness (particle properties) • Diagenesis • Tortuosity
- 3. PERMEABILITY Measurement of permeability: • Laboratory method: passage of fluid through a cylindrical core. Another method uses gas flow under pressure (but this has to be corrected by the Klinckenberg correction) • Direct or field method: measurement takes place by down hole logging. Most commonly used log for this is the Nuclear Magnetic Resonance (NMR) log. Different types of permeability: • Absolute or intrinsic or specific permeability • Effective or phase permeability • Relative permeability NOTE: It is the simplest measure of the producibility of subsurface formations.
- 4. GEOPHYSICS • Geophysics refers to the study of the Earth’s subsurface on the basis of different physical properties. • It covers the fields form the passage of elastic waves within the Earth as well as its electrical, magnetic and gravity fields. • Used by exploration personnel to make predictions about the presence and nature of subsurface hydrocarbon accumulations. • Problem in geophysics: the inverse problem (the non unique nature of the solution for a set of measurements) SEISMIC SURVEY: It employs a source to generate vibrations that propagate into the subsurface. These waves are reflected by the subsurface terrane. These are picked up by geophones. By structural imaging, subsurface layers are identified. The places along which the velocity changes are interpreted to be interfaces between different rock layers. Additional information (characteristics of rock layers) can also be obtained.
- 5. GEOPHYSICS • Records spatial variation in Earth’s gravitational field. • This happens because of difference in density of rocks in the subsurface. • Corrections have to be applied. (Eg. Bouger Correction) • Most common oilfield application is to delineate salt domes (salt domes give a big gravity anomaly due to their lesser density.) ELECTRO MAGNETIC SURVEY: • It works on the basis of the resistivity of the subsurface formations. • For eg. Rocks saturated with hydrocarbons have higher resistivity and can be detected by EM surveys. • Two methods are used for acquiring information: Controlled source EM (CSEM): used in marine settings Magnetotellurics: uses fluctuations in the Earth’s magnetic field induce by solar wind. ( a natural EM source.) MAGNETIC SURVEY: • It relies on the permanent magnetic properties of rocks. Sedimentary rocks generally have a small magnetic susceptibility as compared to igneous or metamorphic rocks. Hence, oil bearing sedimentary rocks can be identified. • Measures subtle anomalies in magnetic field • Covers a large area; used mainly for mineral exploration GRAVITY SURVEY:
- 7. Oil and Gas Exploration Essentials Oil and gas exploration is the search by petroleum geologists and geophysicists for hydrocarbon deposits beneath the Earth's surface. Elements and processes that are essential for the existence of petroleum accumulation:- •Trap:- A barrier to the upward movement of oil and gas • Reservoir:- Porous and permeable to receive the hydrocarbons • Source rock:- A rock formation containing organic matter •Seal:- An impermeable cap to keep fluid in the reservoirs
- 8. Oil and Gas Exploration Essentials • Different personnel perform the task of exploration collectively. Geologists, geophysicists, etc. are all involved here. • Different surface and sub surface techniques are utilized for exploration.
- 9. DRILLING Spudding In:- •The commencement of drilling is termed Spudding in Drilling Ahead:- •Drilling ahead means the actual drilling of the well. Specific drilling processes vary, but many of the work hazards are similar. Tripping the bit:- •Tripping the bit is the physical act of pulling the drill string out of the wellbore and then running it back in. • The mud is circulating to bring cutting and gases up to the surface k/a circulating bottoms up.
- 10. Casing Point • The casing point is the point in a drilling project when well drilling operations cease and the well owners must decide whether the well should be completed or plugged & abandoned. • Casing point may also refer to the depth to which casing is set in a well. Leak Off Test • Leak Off Test is conducted in order to find the fracture gradient of certain formation at casing shoe depth. • The results of the leak off test dictate the maximum pressure or mud weight that may be applied to the well during drilling operations.
- 11. Drilling Fluid – Definition Suspension or emulsion? Emulsion: a mixture of two or more liquids that are normally immiscible (unmixable or unblendable). Suspension: a heterogeneous mixture in which the solute particles do not dissolve but get suspended throughout the bulk of the medium.
- 12. Drilling Fluids Types Drilling Fluid Water Base Mud (WBM) Non-Inhibitive Type Native Mud Bentonite Mud Inhibitive Type Calcium Treated Mud Salt Water Mud Potassium Base Mud KCl-PHPA Polymer Mud Oil Base Mud (OBM)
- 13. Function of Drilling Fluids Remove cuttings from the well. Control formation pressures by providing hydrostatic head. Suspend and release cuttings. Seal permeable formations. Maintain wellbore stability. Minimize reservoir damage. Cool, lubricate, and support the bit and drilling assembly. Transmit hydraulic energy to tools and bit. Control corrosion. Facilitate cementing and completion. Minimize impact on the environment. Drilling Fluids Properties Density Viscosity Apparent Viscosity Gel Strength PV YP Solid Content pH Fluid Loss Chloride Content
- 14. Circulating Components Circulating component consist of the following: 1. Mud Pump 2. Pump Manifold 3. Standpipe 4. Swivel 5. Drillstring 6. Annulus 7. Return Line 8. Shale Shaker 9. Desander 10. Desilter 11. Degasser 12. Mud Pit
- 15. •Rig Monitors •Flame Ionization Detector •Fluoroscope •Chromatograph •Microscope •Mud log computers •Vacuum Oven •Gas analyzer •Porosity Meter •X-ray Diffractometer •Centrifuge
- 18. Perforation • A method of establishing effective communication between the wellbore and the formation • Involves blasting channels for the fluid to flow – detonators serve the purpose Types : Shaped-charge Detonation & Electrical Detonation • Both of the methods make evident use of explosives – when SCD uses only secondary explosives, ED uses primary explosives as well. • Detonators are mounted on a perforating gun.
- 19. • Types of perforating guns: • Perforating Parameters: Shots per foot and phasing • Methods of Perforation: • Selection: The selection of method and type of the gun depends on wellbore geology and other characteristics. For example, the reservoirs with high horizontal permeability require deeper holes whereas the wells producing more sand are compatible with large diameter holes and independent of depth of the holes. Through Tubing Guns Hollow carrier / Casing Guns 1.) Run through the tubing 1.) Tubing is pulled out and gun is run through casing 2.) Uses small sized charges 2.) Houses larger charges 3.) smaller in diameter 3.) comparatively larger diameter Tubing Conveyed Perforation Wireline Perforation 1.) Gun attached to the tubing end and then lowered 1.) Gun is lowered with the help of cable 2.) Drilling/Work-over Rigs are required to lower the gun 2.) Rig is not required 3.) Benefit : leaves the tubing in place after the perforation 3.) Benefit: Accurate depth correlation with CCL 4.) Limitations : Entire tubing has to be pulled out to retrieve the gun 4.) Limitations : Gun Length and Weight
- 20. Reservoir Enginnering • Domain which deals with the evaluation and management. • It employs the combination of various engineering and scientific methods to predict the properties of the reservoir. • Various aspects include: 1.) Reserve estimation a.) Volumetric method b.) Material Balance Methods c.) Decline curve method (semi-logarithemic plot of well prod. Rate v/s time. Type of curves : exponential, hyperbolic & harmonic curves) d.) Comparative Methods
- 22. b.) Reservoir Drive Mechanism Analysis & Drive Indices calculation c.) Reservoir Modelling d.) Reservoir Monitoring e.) Reservoir Characterization – Dry, Retrograde, Wet, Volatile, Heavy oil, black oil Reservoir Engineering deals with various factors such a porosity, permeability, viscosity, compressibility, formation volume factor, PVT analysis to carry out various above given operations.
- 23. What is Cementing ? •Cementing is the process by which cement slurry is placed in the annulus, bonding the casing to the formation. •• The conventional method of doing this is to pump cement down the casing and displace it around the casing shoe into the annulus. • A good cement job is essential to allow further drilling and production operations to proceed. In some cases this can be done in a single operation by pumping cement down the casing, displacing it around the casing shoe and up into the annulus • For conductor and surface casing the whole annulus is cemented back to surface • In longer casing strings (e.g., production casing) the cement job may be carried out in two stages: − the first stage is completed in the conventional manner as described above, with the exception that the cement slurry does not fill the entire annulus, but reaches only a predetermined height above the shoe − the second stage involves opening a special tool in the casing string which allows cement to be displaced from the casing directly into the annulus. This is known as ‘stage cementing’.
- 24. •
- 25. Well Completions • Completion is a technique where equipment's are selected & installed in a well to get optimal production safely for entire foreseeable producing life of a oil or gas well. • The decision to case and cement the well for production or plug it for abandonment can be done only after Formation evaluation using open hole logs. • Completion design is a function of numerous reservoir characteristics, such as - Permeability - Porosity - Saturation Pressure - Stability, and - Compartmentalization
- 26. Well completions Types of completions • Open hole completion: production casing is set on top of the pay zone. • Cased Perforated completion: producing interval is covered by the production casing. • Liner completion: production casing is set on top of the pay zone and is followed by a liner. Factors Influencing Well Completion Selection : • Natural occurrences of the field, i.e. does it have a big reserve to justify development? • Potential of oil production and the planning of tertiary recovery, i.e. do we need any artificial lift in the future? • Limitations within the operation and the field, i.e. is the oil field located at a remote area?
- 27. Reservoir Drive Mechanism •Affected by natural causes—temperature and overburden pressure •Gravity play role in segregation •Drilling causes pressure disequilibrium->maintain by fluid flowing into the well- >fluid movement depends on •Fluid do not move uniformly due to rock and fluid heterogeneity •Primary natural drive systems 1.Water drive (recovery factor 35% to 75% of OOIP) •Comes from connected aquifers •HC extracted ->water drives in a) bottomwater drive(coning) and b) edgewater drive •Waterflood->injection of water for production 1. Water drive 2. Solution-gas drive 3. Gas cap drive 4. Gravity drive
- 28. 2. Gas cap drives (recovery factor 20% to 40% of OOIP) •Due to expansion of gas at top of reservoir-> bubble point •Oil leg->completion of well to avoid producing gas •GOC moves downward->pressure dropped->produced gas injected back. 3. Solution gas drive (recovery factor 5% to 30% of OOIP) •Saturated reservoir ->initial pressure above bubble point •Oil produced->reservoir pressure dropped->expanding gas-> support reservoir and help flow of oil. •If bubble point reached-> decline in oil production->system falls-> liberated gas may migrate 4. Gravity drive (recovery factor 5% to 85% of OOIP) •Gas cap+water drive •Energy from two direction a)Towards upward -- hydraulic pressure in oil columns b)Towards downward – expanding gas column
- 29. RHEOLOGY •Study of how material flow as a function of 1. shear or load rate 2. Time 3. Spatial orientation Affected by MANY factors 1. Temperature 5. Drilling fluid 2. Pressure 6. Cement 3. Rate and duration of shear 7. workover fluid 4. Production fluid 8. completion fluid • Affect negatively 1. heavy oil production high viscosity diff. to produce 2. Deepwater cooler environment create flow problem • Viscosity, shear stress (shear rate)
- 30. Rheology models Types of fluid flow 1. Newtonian viscosity dir. por. to shear stress 2. Non-Newtonian a. Bingham plastic not flow until yield point b. Power law shear stress const. exponential good fit at low shear stress no yield point ,no gel strength c. Hershcel Bulkey models addition of above two. • Non –Newtonian fluid is useful Thixotropic Fluids ongoing increase in gel strength depend on rest time • Used in wells in which fractures and lost circulation are concern
- 31. Well logging
- 32. Type of well logging
- 33. Gamma ray
- 35. Density & Neutron Porosity
- 36. Electrical log
- 38. DEFINING POROSITY • Porosity – is volumetric void spaces present in a rock, 2 types • Permeability – is the ability to allow fluids to pass through it • First formation resistivity is calculated which helps to identify the HC bearing rock • NOTE • Resistivity high HC bearing rock • Resistivity low Water bearing rock
- 39. • Sonic porosity - Calculated by using speed of sound • Density porosity - Emits medium range of gamma rays - Gamma ray hits the e- in formation - e- density is directly proportional RHOB - density porosity is calculated by • Neutron porosity - High energy(10^6 eV) fast neutron bombardment - Energy loss takes place while collision with formation nuclei and reaches to thermal energy state - Energy loss is correlated with relative mass of the nuclei POROSITY MEASUREMENT
- 40. • Thermal Energy state- At this state only few thermal neutrons come back to detector and rest of them captures. • Then the counts at detector is calculated which is used to measure Hydrogen index • Finally we calculate neutron porosity using HI Generally • Reservoir rock – having hydrogen associated with Liq. (Oil/Water) in pore spaces • Gas – generally gas has low Hydrogen density than oil/water • High H-atoms means less counts at detector • Low H-atoms means high counts at detector
- 41. CROSS-OVER Tells about the fluid type and lithology • Cross plot porosity or Total porosity - is calculated using neutron and density porosity
- 42. • Porosity can also be calculated by NMR tools (calculates directly the liquid filled porosity) and core sampling (provide empirical porosity which can be different from actual porosity) • Porosity tells the HC potential so that best recovery of HC can be achieved
- 43. Well Testing Fundamentals • Done while flowing fluid from the reservoir • This test is to determine whether a formation will produce HC @ rate of reasonable return with further investments • During testing : Formation Pressure, K, Skin (damage to the formation during drilling or other well operation) is calculated • Production potential test can be performed through different methods • A) Production well test • B) Drill Stem Test • C) Wireline Formation tester
- 44. A. Production well test • In this well is flowed through a test separator. • Deflector plate - slow down the flow vel. • Coalescing plate - gather oil into large droplet • Separator sector • And as the pressure reaches bubble point pressure or below that, gas start evolving from oil • Mist extractor • And using pneumatic valves gas and fluid exit is controlled and flow rate is measured using orifice plate meter
- 45. B. Drill Stem Test • During production • Formation fluid is flowed through drill string to the surface @ different rates through choke valves (controls flow rates) • Pressure variation curve is plotted vs. time Pressure Test Types 1. Buildup -Pressure rise is recorded @ bottom hole in shut-in condition 2. Drawdown – well is opened and BHP start decreasing 3. Falloff/Injection – fluid is injected into formation , BHP increases 4. Interference – as the well shut-in the BHP start decreasing is monitored & recorded. And the time gap gives an indication of reservoir size & flow communication
- 46. • For measuring this time change a technique called Transient analysis technique is used. It uses a mathematical correlation of formation pressure, flow rate and time. It leads to conclude i. HC potential, skin ii. K, reservoir boundary shape and distance from the wellbore iii. Initial & Avg. reservoir pressure • Collectively these pressure tests are called drill stem test • Isochronal Test - Series of drawdown & buildups - pumping rate vary for each drawdown , while buildup continue until the well reaches its original shut in period • Modified Isochronal test – Both drawdown & build up periods are of equal duration • These tests also give the information of Production potential, K, skin and AOF(absolute open flow)
- 47. C. Wireline Formation Tester( WFT) • Captures fluid sample and measure press. Downhole at the zone of interest • Quartz pressure gauge – measure pressure • Probe – use to suck formation fluid • Packer assembly – supports the probe • Sample chamber – use to collect and analysis • Pump – controls the backpressure and using control valves diverts the contaminated fluid into wellbore and uncontaminated to sample chamber • DFA (Downhole Fluid Analysis) – To measure GOR and to monitor sampling process • Optical Spectroscopy – It identifies the fluid composition • Well test data has application to correct the reservoir models, which allows operators to make better long term decisions about their assets
- 48. Downhole Coring • Coring is process of obtaining an actual sample of a rock formation from the borehole and provide essential data for the exploration ,evaluation and production of oil and gas reservoirs. • Core provide ground truth of calibration of well logs. • Production can be optimized based on the analysis of core porosity ,permeability, fluid saturation ,grain density , lithology and texture. • Core samples can be undertaken in two ways: • 1.Conventional Coring: It is performed when Zone is being drilled.It is similar to Conventional drilling and chiefly differe in types of bit used. • First well is drilled using conventional drill bit and drill string and a wellsite geologist closely monitors drilling progress to decide when to begin coring operations.The time of this decision is critical. Correlations with offset well logs usually provide the first indication that the drill bit is nearing the coring point. Once the geologist gives the order to begin coring, the driller pulls the drill bit out of the hole, and the drilling crew exchanges the drilling BHA for a coring bit and core barrel. •
- 49. 2.Sidewall coring :Sidewall cores (SWCs), plugs of rock taken from the wellbore wall, may offer a cost-effective alternative to conventional cores. After the driller reaches a casing point or drills to total depth (TD), the drillpipe is pulled out of the hole and the well is logged before casing is set. Sidewall cores typically are obtained after logs have been run, usually near the conclusion of an openhole wireline logging job. Two types of wireline sidewall coring devices—percussion and rotary—are available. A percussion coring tool, or core gun, has bullet-shaped core barrels mounted on a carrier (below). The core gun uses small explosive charges to propel individual core barrels into the side of the wellbore to capture samples of the formation. In contrast, a rotary coring tool uses a small, horizontally oriented coring bit to cut plugs from the side of the borehole (below).
Editor's Notes
- #32: 9639193290