PROPOSAL - Integrated Subsurface Desc

7/23/2019 PROPOSAL - Integrated Subsurface Desc

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PROPOSAL

A hydrocarbon reservoir needs to be managed properly with a thoroughunderstanding of its characteristics to maximize the economic recovery of hydrocarbon accumulation from a eld. Field X has been producing undernatural drive for 10 years. atural depletion is often insu!cient and withreservoir pressure decreasing" it has to be articially maintained throughwater#ooding.

$n order to form an e%ective water#ooding design for eld X" followingsteps must be carried out&

'omprehensive reservoir description" identication of #ow units"observation and interpretation of production history ()istory matching*"drilling and completion data from existing wells" laboratory analysis"

development and +ustication of reservoir models" assessment of ,what-ifsituations" pilot pro+ects and economic analysis.

/he essential data reuired are the reservoir geometry depth" lithology"porosity" permeability" continuity of roc2 properties" #uid saturations" #uidproperties relative permeabilities and" water source its chemistry.



Faults may extend over several hundreds of kilometres or may be restricted to the

deformation of individual grains. They create vast potential traps for the accumulation of oil

and gas. However, they often dissect reservoirs and seal fluid and pressures in numerous

individual compartments. Each of these isolated blocks may require individual dedicated

wells for production and inection. !eservoir compartmentalisation through small-scale

faulting can thus severely downgrade the profitability of a field under development. "n the

worst case, faulting is not detected until development is in an advanced stage. Early #$

seismic surveys will help to obtain a realistic assessment of fault density and possibly

indicate the sealing potential of individual faults. However, small%scale faults with a

displacement &throw' of less than some ()*+ m are not detectable using seismic alone.

eostatistical techniques can then be used to predict their frequency and direction.



The collection of representative reservoir fluid samples is important in order to establish the

-T properties ) phase envelope, bubble point, Rs and Bo ) and the physical properties )

composition, density and viscosity. These values are used to determine the initial volumes of

fluid in place in stock tank volumes and the flow properties of the fluid both in the reservoirand through the surface facilities, and to identify any components which may require special

treatment, such as sulphur compounds.

!eservoir fluid sampling is usually done early in the field life in order to use the results in the

evaluation of the field and in the process facilities design. /nce the field has been produced

and the reservoir pressure changes, the fluid properties will change as described in the

previous section. Early sampling is therefore an opportunity to collect unaltered fluid

samples.

Fluid samples may be collected downhole at near%reservoir conditions, or at surface.

Subsurface samples are more expensive to collect, since they require downhole samplingtools, but are more likely to capture a representative sample, since they are targeted at

collecting a single%phase fluid. 0 surface sample is inevitably a two%phase sample which

requires recombining to recreate the reservoir fluid. 1oth sampling techniques face the same

problem of trying to capture a representative sample &i.e. the correct proportion of gas to oil'

when the pressure falls below the bubble point.

PVT analysis

6.2.7. Properties of formation water

6.2.8. Pressure–depth relationships

6.2.9. Capillar pressure and saturation–hei!ht relationships

6.".2. Corin! and #ore analsis

Routine core analysis of plugs will include determination of

-orosity

hori2ontal air permeability

fluid saturation

grain density.

SCAL will include measurements of

electrical tests &cementation and saturation exponents'

3relative permeability

3capillary pressure

3strength tests.

Mudlogging is another important direct data gathering technique. The returns to surface &drill



cuttings and gas levels' and !/- are continuously recorded and analysed to establish the

nature of the formation and fluid fill.

4idewall samples are useful to obtain direct indications of hydrocarbons &under 5 light' and

to differentiate between oil and gas. The technique is applied extensively to sample

microfossils and pollen for stratigraphic analysis &age dating, correlation, depositionalenvironment'. 6ualitative inspection of porosity is possible, but very often the sampling

process results in a severe crushing of the sample, thus obscuring the true porosity and

permeability.

"n a more recent development a new wireline tool has been developed that actually drills a

plug out of the borehole wall. 7ith sidewall coring &Figure 8.#(', some of the main

disadvantages of the 474 tool are mitigated, in particular the crushing of the sample. 5p to

9+ samples can be individually cut and are stored in a container inside the tool.

http://www.sciencedirect.com/science/article/pii/S0376736107000064#fig35

http://www.sciencedirect.com/science/article/pii/S0376736107000064#fig35



6.".$. Lo!!in!%measurement while drillin! &L'(%)'(*

7hilst providing deviation and logging options in high%angle wells is a considerable benefit,

the greatest advantage offered by :7$ technology, in either conventional or high%angle

wells, is the acquisition of real time data at surface. ;ost of the :7$ applications which are

now considered standard, exploit this feature in some way, and include

real time correlation for picking coring and casing points



real time overpressure detection in exploration wells

real time logging to minimise <out of target= sections &geosteering'

real time formation evaluation to facilitate <stop drilling= decisions

Indicators of these factors come from logs, labrotary and field tests, productions history,cores taken during drilling, and seismic profiling.

The simulation begins with basic reservoir analysis to highlight essential parameters for the

simulation. This involves volumetric analysis, estimate fluids in place, fluids properties, wells

specification and faults that may exist.

It is vital before any development plan is created that thorough analysis of the reservoir datais carried out. This enables the user to fully appreciate the characteristics of the model,making interpretation of later results much simpler.

To accurately assess a reservoir towards development, knowing and appreciating the sizeand type of reservoir formation and fluids being dealt with is an extremely important aspect.

Understanding the type of formation lithology and reservoir fluid is undoubtably the mostimportant concept in relation to creating a successful development plan. From data filescontaining porosity and permeability values called porovancouver! and "ermvancouver!respectively,

#fter fluid analysis from the reservoir model data sheet, no gas exists in the system, hencethe fluid was assumed to be dead oil, this was confirmed through the "$T properties used inthe reservoir.

0-" value must be deteremined to identify the type of oil. 0-" chart

#ny fluid in a reservoir which is being produced will be sub%ected to different forces such asgravity, capillary pressure and viscosity. &hen a reservoir contains more than one fluid,surface tension and wettability effects will act to try and minimise the energy that is 'lockedup( over fluid and solid interfaces. )enerally, smaller capillary pressures re*uire less energythan higher capillary pressure for the non+wetting phase to migrate. The model has relativelyhigh capillary pressure from up to - psi with / residual oil saturation which can only be

reduced through enhanced recovery. It was observed that this model doesn(t exhibit a*uifer drive, which can be seen from 0rror1 2eference source not found, where the residual oilsaturation is not reached at a capillary pressure above psi, indicating no potential a*uifer drive. The initial water saturation was .34 and oil formation volume factor(s range from 5+.63.

7ut using the residual saturations and given capillary pressures, it was possible to identifythe wettability of the formation rock through using the #mott method as shown in 0*.+4below.

8ore samples are excavated with the aim of determining whether a find will be commercial.



The historical production and pressures are matched as closely as possible through alteringparameters in a mathematical model of the reservoir, reproducing alternate realisticbehaviors for the reservoir in production data 9:;. This method is typically defined as aninverse problem, where final data sets such as production are used to define the data setsthat characterised them initially, such as permeability and porosity. The accuracy of thehistory matching however strongly depends on the *uality of the reservoir model and the*uality and *uantity of pressure and production data given. <nce a model has been historymatched, it can be used to simulate future reservoir behavior with a higher degree ofconfidence, particularly if the ad%ustments are constrained by known geological properties inthe reservoir.

"lacement of both in%ector wells and producers were largely determined through analysis of porosity and permeability distribution in the = grid models provided through Flo$iz shown infigures 3+4. The methodology was to input producing wells into areas of high porosity and

permeability, with in%ectors surrounding these areas in the most effective formation to reduceisolation of any oil bearing sections.

These types of wells are normally largely dependent on formation thickness and are mosteffective in shallow reservoirs of around 5 ft 955;. &hen under these conditions can maintainthe same production rates as vertical setups but at much lower pressures, and with theability to1 cover larger areas in a formation, increase production>in%ection rates and sweepefficiency, theoretically considerably fewer horizontal wells for both production and in%ectionare needed compared to vertical.



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PROPOSAL - Integrated Subsurface Desc