Introduction

Abstract

Petroleum Engineering is a broad discipline with several areas of specializations such as petroleum geology, petrophysics, drilling engineering, mud and cementing, reservoir engineering, production (surface & subsurface) engineering, completion, formation evaluation, economics etc. These specialized areas work together as an integrated team to achieve one goal; to recover the hydrocarbon in a safe and cost-effective way. Petroleum engineering is one of the key aspects of Engineering that is concern with the exploration and production of hydrocarbons for consumption by human or to meet the host countries or global energy needs. This chapter presents an understanding of the essential features of petroleum reservoir, the job description of a reservoir engineer, the concept of drainage and imbibition processes, the hydrocarbon phase envelope and all its terminologies, identification of various types of reservoir fluids and their respective phase envelope/diagrams, understanding of the types of fluids in terms of flow regime and reservoir geometry and write the mathematical equations representing the flow regimes. Thus, for a better understanding of the flow regime, several solved example questions are given.

Exercises

• 1. Mention the three ways rock can be formed and which of them forms the largest share of the rocks on the earth’s surface?.

• 2. List the key elements required to define a petroleum reservoir

• 3. Differentiate between a cap rock and a real

• 4. Rivers have been washing gravel, sand and mud down into Sydney harbour for thousands of years. Deep in the ancient deposits these materials have been packed down by the weight of overlying layers and pore spaces have been in-filled by cement-like carbonate minerals. Are the rocks that are forming Igneous, Sedimentary or Metamorphic? Justify your answer

• 5. The ore body at Broken Hill was found associated with layers of rock that frequently consisted of interbedded quartzites and garnet schists. Are they Igneous, Sedimentary or Metamorphic rocks and why?

• 6. Distinguish between drainage and imbibition process

• 7. In one phase envelop diagram, draw the following: black oil , volatile, condensate, wet and dry gas reservoir .

• 8. What is the term that defined the phase in the development of a petroleum system during which hydrocarbons migrate into the porous and permeable rock formation (the reservoir) and remain trapped

• 9. When the capillary pressure across the pore throats is greater than or equal to the buoyancy pressure of the migrating hydrocarbons. What term is this?

• 10. Which of these is not associated with fault: single, parallel, perpendicular, sealing and non-seal

• 11. Which of these is not a process that culminate into trap : formation of anticlines, folds, syncline and domes

• 12. A fluid flow process in which the saturation of the nonwetting phase increases.

• 13. Which concept defines a case when the mobility increases with saturation of the nonwetting phase?

• 14. A fluid flow process in which the saturation of the wetting phase increases.

• 15. When mobility increases with saturation of the wetting phase. The term is called

• 16. The classification of a hydrocarbon reservoir is basically dependent on the following except:

  • The composition of the hydrocarbon mixture in the reservoir,

  • The amount of the fluid in place,

  • The location of the initial pressure and temperature of the reservoir and

  • The condition of the surface (separator) production pressure and temperature.

• 17. A phase envelope or pressure-temperature (PT ) phase diagram of a particular fluid system comprises of two major curves. These are

• 18. How many types of reservoir can be identified beyond the dew point curve? Name them.

• 19. The region where gas and liquid coexist in equilibrium is called

• 20. The region of quality lines identified in a pressure-temperature diagram is called

• 21. A reservoir whose fluid remains as a single phase liquid at the wellbore is called

• 22. What type of reservoir is identified when the pressure and temperature conditions existing in the separator indicate a high percentage of liquid around 85%

• 23. A black oil is often called

• 24. Which reservoir is characterized by a dark or deep color liquid having initial gas-oil ratios of 500 scf/stb or less, oil gravity of 30° API?

• 25. Which reservoir is characterized by a brown, orange, or green color liquid oil gravity of 40° API or higher and 65% of the reservoir is liquid at the separator condition

• 26. What is the range of a gas condensate reservoir’s API oil gravity?

• 27. A gas reservoir whose production path passes through the two phase region is called

• 28. A fluid whose volume or density does not change with pressure is called

• 29. Which fluid experience large changes in volume as a function of pressure

• 30. When fluids move in a multi-direction within the reservoir towards the perforations at the wellbore creating an iso-potential lines. What type of flow system is this?

• 31. A system of mass flow rate, where there is no accumulation of mass within any component in the system is called

• 32. The flow of fluid across the boundaries of the reservoir

• 33. What type of flow is experienced in an unbounded reservoir?

• 34. Give an example of an incompressible fluid

• 35. Which parameter causes an additional pressure drop near the wellbore?

• 36. Skin is a reservoir phenomenon, true or false give a reason for your answer

• 37. Skin accounts for

• 38. A state where the mass rate of production is equal to the rate of mass depletion is termed

• 39. One of the conditions necessary for pseudo steady state to be attained is that reservoir outer boundary must be closed to flow. True or False, give reason for your answer

• 40. When a well that attains steady state is shut in, the pressure does not build up to average pressure. The pressure builds up to initial pressure because of

• 41. A reservoir attains pseudosteady state if the rate of pressure decline is constant. And the constant is related to

Ex 1.1 :

Given the following data:

Wellbore radius, r w	0.3728 ft
Drainage radius, r e	1100 ft
Reservoir height, h	37 ft
Initial pressure,P i	4200 psi
Pressure at the outer boundary, P e	3640 psi
Bottomhole flowing pressure, P wf	2800 psi

Calculate

• I. The reservoir pressure at a radius of 67 ft

• II. The pressure gradient at 67 ft

Ex 1.2 :

An oil well is flowing at 230 stb/d from a uniform sand under steady state with the following data:

Total compressibility, S wc	23%
Reservoir height, h	32 ft
Static Bottomhole pressure, P ws	2500 psi
Formation permeability, k	242 mD
Oil viscosity, μ o	0.59 cp
Oil formation volume factor, β o	1.342 rb/stb
Porosity, ∅	22%

• I. What is the pressure at 20 ft radius using a 560 ft drainage radius?

• II. What is the pressure drop using the 560 ft drainage radius and wellbore radius of 5 inches?

• III. Compare the pressure drop from 560 ft to 95 ft with that from 95 ft to 10 ft.

• IV. What is the pressure gradient at 28 ft

• V. What is the actual average radial velocity at 28 ft?

• VI. How long will it take oil at 560 ft radius to reach the wellbore?

Ex 1.3 :

A gas well is producing under the following conditions:

Wellbore radius, r w	0.385 ft
Drainage radius, r e	980 ft
Reservoir height, h	28 ft
Reservoir temperature, T	150 °F
Initial pressure,P i	1700 psi
Bottomhole flowing pressure, P wf	1450 psi
Formation permeability, k	45 mD
Gas gravity, γ g	0.62
Skin factor, s	1.06

Calculate the gas flow rate using:

• I. Pressure-square approximation

• II. Real gas pseudo-pressure approach

Ex 1.4 :

An oil well producing at a constant rate of 350 stb/day under unsteady state flow conditions. The reservoir has the following rock and fluid properties:

Wellbore radius, r w	0.5 ft
Total compressibility, C t	7.45*10 −6 psi −1
Reservoir height, h	20 ft
Initial pressure,P i	4200 psi
Formation permeability, k	80 mD
Oil viscosity, μ o	1.48 cp
Oil formation volume factor, β o	1.275 rb/stb
Porosity, ∅	18.5%

Calculate the pressure at the following radius 0.67 ft, 6 ft, 12 ft and 115 ft after 2 h of production.

Ex 1.5 :

Given the following data of a well in an infinite acting reservoir.

Wellbore radius, r w	0.3512 ft
Drainage radius, r e	850 ft
Total compressibility, C t	3.6 * 10 −6 psi −1
Reservoir height, h	46 ft
Initial pressure,P i	3250 psi
Formation permeability, k	154 mD
Oil viscosity, μ o	0.759 cp
Oil formation volume factor, β o	1.3023 rb/stb
Porosity, ∅	25%
Oil flow rate, q o	498 stb/day
Time, t	7 h

• Calculate the wellbore flowing pressure at a distance (radius) of 60 ft after 7 h production.

• The wellbore flowing pressure at a distance (radius) of 118 ft after 7 h production

• The wellbore flowing pressure at a distance (radius) of 217 ft after 10 h production

  Ex 1.6 :

  Calculate the gas flow rate of a gas well with average reservoir pressure of 2100 psi and bottom hole flowing pressure of 1200 psi using pressure-square method.

  Additional Data:

Wellbore radius, r w	0.451 ft
Drainage radius, r e	945 ft
Reservoir height, h	33 ft
Reservoir temperature, T	175 °F
Formation permeability, k	238 mD
Gas gravity, γ g	0.74

Ex 1.7 :

Given the following data:

Wellbore radius, r w	0.45 ft
Drainage radius, r e	810 ft
Total compressibility, C t	3.23 * 10 −6 psi −1
Reservoir height, h	31 ft
Pressure at the outer boundary, P e	3700 psi
Bottomhole flowing pressure, P wf	2780 psi
Formation permeability, k	140 mD
Oil viscosity, μ o	1.24 cp
Oil formation volume factor, β o	1.148 rb/stb
Skin factor, s	4

Calculate the oil flow rate assuming that the fluid is slightly compressible. Also compare the result with assuming the fluid is incompressible.

Ex 1.8 :

A producing well is located some 1500 ft away from an observation well, both near the center of a circular drainage area of radius, r_e = 1000 ft. If the producing well is flowing at the rate of 1200 stb/d, calculate:

• I. The resulting pressure drop at the observation well

• II. The pressure drop at the observation well if it produces at the rate of 800 stb/d

• III. The total pressure drop if both wells produce at 1000 stb/d each.

  Additional rock and fluid properties are:

$$ {r}_w=4\ inches,\kern0.5em h=77\ ft,\kern0.5em k=480\ mD,\kern0.5em {B}_o=1.462\ rb/ stb,\kern0.5em {\mu}_o=0.68\ cp, $$