Olkaria III Field Development - Hagen Vs

8/10/2019 Olkaria III Field Development - Hagen Vs

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Geotherm al Resources Cou ncil Transactions,Vol. 2

6,

September

22-25, 002

Olkaria

111

Field Develop m ent

Hagen Hole and

Uri

Kaplan2

Geothermal Consultants New Zealand Ltd.

20RMAT International, Inc.

Keywords

Kenya, Olkaria

Ill

dimensional numerical model, ear ly

generat ion plant , ORMAT Energy Converter

ABSTRACT

The Olkaria 111geothermal project is the first private geo-

thermal project in Kenya. The field development of the project

was managed by ORMAT geothermal group and included flow

testing of wells drilled in the past by a subsidiary of the Kenya

National ElectricityAuthority - Kenya Power Company (KPC);

field analysis including a three-dimensional numerical simula-

tion model of the reservoir and the successful drilling of nine

new wells. The field development is a combined effort of

ORMAT and some of the leading geothermal engineering groups

worldwide.

In parallel with the field development, ORMAT constructed

an early generation power plant based on binary type

ORMAT@ nergy Converters (OECs) which, in addition to the

generation and sale of electricity at an early stage of the project,

has enabled testing of old and new wells for an extended period

of time. This has allowed for on-going and continuous updating

of the field parameters during the conceptual design and de-

tailed engineering phases of the project.

Introduction

OrPower 4, a special purpose project company, has secured

the right to develop and operate the Olkaria

111

geothermal de-

velopment concession within the Rift Valley in Kenya. This

concession has an area of approximately 12.4 km2 and encom-

passes the West Olkaria geothermal resource which was first

confi ied to exist with the drilling of exploration well OW-

301 in 1983.

The Olkaria

111

(West Olkaria) area lies 3 km to the west

of the

45

MWe Olkaria I (Olkaria East) geothermal develop-

ment area where the first 15 MWe unit came on line in June

1981 and the third and final unit started operation in March

1985. OlkariaI is operated by the Kenya Electricity Generating

Company Ltd. (KenGen) {previously Kenya Power Company

(KPC)}, who are also currently developing the

2 x

32 MWe

Olkaria I1 project (Northeast Olkaria), which lies immedi-

ately north of Olkaria I and extends to within 2 km of the north-

east boundary of the Olkaria 111concession.

In July 1996, in an effort to develop the current power gen

eration potential of Kenya, the Government of Kenya GOK

conducted an international tender for a build, own and operat

contract (BOO) geothermal power facility within the Olkaria

111area as described above.

In November 1998, the Olkaria

111

tender was awarded to

ORMAT International, Inc. and ORMAT, through OrPower 4

as a special purpose company for the project, entered into a

20

year Power Purchase Agreement (PPA) with Kenya Powe

and Lighting Company (KPLC), Kenyas sole electricity dis

tributor. The Olkaria111project consists of two phases.

Phase I, which has been already completed, involved the

construction of a 13.5 W plant, which was constructed on

a

fast track to provide early generation and long term well flow

data for on-going resource assessment. Phase I1 is the expan

sion to the full technically feasible plant capacity of the resource

Under the PPA, KPLC is required to make capacity and en

ergy payments to ORMAT, based on prices that were fixed in

ORMATS economic bidding proposal under the RFP.

An integral component of Phase I1 was a resource assess-

ment study which included a 3-dimensional numerical mode

of the Olkaria

III

field. This study was a combined effort in

volving the leading geothermal groups PB-Power of New

Zealand, Orkustofnun of Iceland and GeothermEx of the USA

In addition, KenGen (the Kenya Electricity Generating Com

pany Ltd.) supplied a significant amount of information regard-

ing the Olkaria 111 field and have contributed to the project in

conducting well testing, data review and interpretation, as wel

as

providing other professional services. The resource assess-

ment study was conducted in parallel with the drilling of new

wells with new information gathered during drilling and testing

of these wells being incorporated into the resource models as

well as being used as a tool for re-calibration of the model. The

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Hole and Kaplan

results of this study allowed for a decision on the power plant

capacity target to form the basis for OrPower 4s obligation in

the Power Purchase Agreement with the Government of Kenya.

Wells Drilled Prior to

ORMAT

Involvement

The development of Olkaria I11 geothermal field was started

by KenGen in 1983 and 9 wells were drilled to depths of 1900

to 2500 meters

within

the concession area by 1991. These are

vertical wells, drilled with water, aerated water and in some

cases mud. The permeability of some of the wells is relatively

low and in the case of well OW-305 skin damage is evident as a

result of using mud as drilling fluid within the production zone.

Only wells OW-30l,OW-303A (now abandoned) and OW-305

were clearly within the main productive reservoir. The other

wells that lie close to the concession borders, are significantly

cooler than the more central wells and some have temperature

inversions that indicate they are in outflow or cold water inflow

areas. Of these marginal wells OW-302 and OW-401 have some

useful discharge (well OW-302 is cyclic) and connecting them

to the power plant is in question.

In 1998 OrPower 4 initiated retesting of the producing wells

OW-301,OW-302,0W-305 and OW-401

in

order to study the

present characteristics of the wells and changes in the produc-

tivity

since the time they were drilled and initially tested. The

test results formed basis of the design of the early generation

plant and were used for the field analysis and building

of

the

three dimensional numerical model.

Table 1 summarizes the

test results of the 4 tested wells.

Table 1. Flow test results.

(KenGen ormerly KPC) and PB Power, GENZL Division,

the tasks of developing a conceptual model and a development

strategy for the Olkaria

111

Concession area.

The resource conceptual models developed by these two

groups, which were both based on the same data collected from

the original KPC exploration program, were similar and identi-

fied a shallower (1500

800

masl) 2-phase zone with good

horizontal permeability, and centred

in

the eastern half of the

Olkaria 111Concession area. The temperatures in this zone were

generally indicated to be in the 220 240C range.

The models also postulated the existence of a deep high tem-

perature reservoir, from which fluids upflow

in

the centre of the

concession area to feed the shallower 2-phase system. The deep

reservoir fluids, as indicated from samples from Well OW-305,

are neutral pH, sodium chloride (530 ppm chloride)

with

a very

low gas content and indicated temperature of around 320C.

The system is predominantly bounded on the east by the

two parallel north-south trending fracture zones he Narasha

Fracture zone,

and the 1 Olbutot Fracture zone.

It is sug-

gested that the zone between these two north-south fracture zones

acts as a conduit at deeper levels for cooler north to south fluid

flow. Wells such as OW-401, OW-202 and OW-203 indicate

these cooler fluids at depth and certainly indicate the eastern

limits to the West Olkaria reservoir.

No

such physical boundary exists to the west, however pro-

duction from the western exploration wells show extreme levels

of non-condensable gases (predominantly C02), suggesting that

production derived from wells drilled within the western half (west

of Well OW-301) would probably be uneconomic (see Table 2).

The C02concentrations measured during the initial production

tests of the western exploration wells within the

Olkaria L concession area were as follows:

Well

No.

WHP Mass Water Steam Enthalpy

Power

Regional west to east, and north to south hydro-

(Bara)

fir)

(fir) (fir) HAP)

(MWe) logical gradients drive the geothermal fluids to the

OW-30 6.4 100.3

50.1

43. I647 4.8

east, and to a lesser extent to the south. The fluids

OW-30

1

9.2

97.7 47. 43.9 I597

4-9

in

the shallow reservoir are high enthalpy and 2-

49

phase, which condense to hot liquid

in

the more dis-

W-30 11.3 96.4 45.4 44.4 1612

OW-30

1

7.4) 105.4) 46.4) 49.

I

1665) 5.3)

OW-302

6.56 53.40

37.10 11.85

1

I08 1.32 tant outflow zones. The shallow reservoir pressure

OW-302 7.79 39.05

26. I6 9.65

1

I62 1.07 corresponds to a water table at about 1500 1700

3.13) 29.6) 1 1 .1 I 6.7) 1 830) masl or about 400 600

m

depth. This significant

W-305

OW-305 3.82 26.5 7.3 16.5 2121

OW-305 5.66 4.94) 20.9 2 1.3) 7.4 5.0) 12.3 15.3) 1886 2149) .4 level of under-pressure, relative to the surface sug-

OW-305 9.4 8.73) 26.0 21.7) 7.6 5.8 16.9 14.7) 201 3 207 I .9 .6) gested high pressure losses will be incurred by liq-

OW-40

1

4.59) 76.7) 53.1)

I

7.3)

I

114)

uid dominated, lower enthalpy fluids travelling up

the well bore.

W-40

1

4.67 62.7 46.4 10.9 1045

Conceptual Model

The Olkaria

111

Concession area is located centrally within

the West Olkaria area which may be broadly defined as that

area west of the

1

Olbutot Fracture Zone within the Greater

Olkaria Geothermal Resource area. West Olkaria was the sub-

ject of a series of geoscientific exploration surveys which were

carried out during the late 1970s and early 198Os, and of an

exploration drilling program which was carried out between

1983 and 1994. This exploration program was executed by the

then Kenya Power Company (KPC).

During the first half of 1999 ORMAT Industries Ltd. as-

signed both the Kenya Electricity Generating Company Ltd.

Figure

I

indicates the extent of the shallow reser-

voir and the top of the deep reservoir as postulated by the con-

ceptual models.

The conceptual models indicated temperatures at 200 masl

(typical well depth of around 1800

m)

range between 230 to

320C with the highest temperatures occurring in well OW-305

Table 2. C 0 2 ConcentrationsofWestern Wells.

Weight C 0 2

Wel l Date Measured in steam

E n t h a l w k l k g

5

bara)

OW-301

2 1.4.99 1572 16

OW-304D

18.6.92 2212 43.9

OW-308

2.12.98

I800 64

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Hole

and

Kapla

I

nrat inn

Im\

Figure

1 .

Shallow and Deep Reservoirs.

in the centre of the eastern half of the concession area. The ex-

ploration wells in the Concession area (other than well OW-

401)generally indicate increasing temperature with depth, with

near isothermal conditions through the shallow reservoir zone

(1500 800masl) indicating good vertical permeability. How-

ever, the temperature gradients below this depth range are typi-

cally conductive suggesting that the deeper zone permeabilities

are not high.

Geothermal fluids from the deep, high temperature reservoir

zone rise in the centre of the eastern half of the Concession area,

through limited permeability, into the shallower reservoir which

has good vertical and horizontal perme-

ability. The models suggested good 2

phase high enthalpy production would

be obtained from wells drilled into the

zone centred on

this

postulated upflow.

Figure 2 presents a summary cross-

section through the conceptual model.

Dri l l ing

New

Wells

Phase I in the well drilling program

was commenced in February 2000,uti-

lizing Nabors Drilling International

Limited of USA as drilling contractor,

with the drilling of five new wells as

part of the field appraisal program as

defined by the tender issued by the

Government of Kenya

GOK),

fol-

lowed by Phase

I1

drilling, he comple-

West

25001

Legend

wells

oads

aults

Fracture

Eruptive

Warm

Probable

a kon

Are

Kongoni

500

1000

ORPOWER

Olkaria

Geothermal

J

tion of drilling activities to supply th

power plant steam and brine require

ment. The PPA contract with

GOK

calls for field capacity capable of sup

plying 120 of plant requirements t

allow for degradation of well produc

tion and well shut-down for mainte

nance.

The drilling approach has been t

drill from a small number of well pad

in order to minimize the surface dis

turbance. Olkaria I11 is located withi

a national park and is home to man

animals. One well on each pad is a ver

tical well, while the others are direc

tional with a lateral target distance o

at least

300 m

to minimize interfe

ence.

The new well drilling program

called for drilling with foam or aerate

water only

as

drilling fluid once dril

ing fluid circulation had been lost, an

in particular within the production sec

tion of each well.

It is evident that as a result of this d

rectional and low density drilling flui

program, along with comprehensivenumerical modeling and analy

sis, that on average, better well productivity has been achieve

compared to wells drilled previously within the greater Olkar

system.

During the period of February

2000

to March

2001

five ex

ploration/production wells were drilled, completed, and tested

satisfying the primary Phase I objectives. In addition to thes

primary objectives, secondary objectives were to prove the ex

tent of the identified shallow 2-phase production zone; and t

drill beyond this shallow zone to identify the postulated dee

reservoir.

East

1

2000

1500

1 000

500

0

500

I

192000 192500 193000 193500 194000 194500 195000 195500 196000 196500 197w)O 197500 191

Location

E m)

Figure

2

Schematic Cross-section Through West Olk aria.

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Hole

and Kaplan

flow

through a horizontal discharge pipe-

line; a Russell James lip pressure pipe;

and into an atmospheric cyclone separa-

torhilencer fitted with a weir box to al-

low monitoring of the separated water

LoceUon E

m)

Figure

3. Olkaria

111

Well Locations.

Available Available Total

Stestm Water TotaIF30 WCG Themat Thennal

Available

~~~~~~

Power Thermal

Steam Water Power apc

W S

W S )

Mwe

Weit

P,,E t , M u w ,

How Mass

Flow

Enthalp;

gvt

) Power

Barn)

barn)

W t ) OIMWt Mwt)

occurred.A range of discharge

WHPs were then tested, each

for a period of around 5 to 7

days, allowing a well discharge

characteristic to

be

plotted. A

summary of the production

discharge data produced from

these tests is presented in Fig-

ure

4.

Conclusion

The Olkaria III field devel-

opment program met all its

planned goals as far

as

budget

and timetable were concerned.

The average productivity

achieved from each of the

wells exceeded initial expecta-

tions and as a result a reduced

number of wells were required

to be drilled to support the

power plant as planned.

It is considered that the pri-

mary reasons for the better

than expected results were

~ombining f pe~odically p-

dated the field modeling with

During the period March 2001 to March 2002, four addi-

tional wells were drilled, completed and tested, and two wells

were commenced but not completed. See Figure

3

for well lo-

cations.

The production success rate of the wells was far in excess

of expectations, hus allowing termination of the drilling opera-

tions in March

2002.

Kenya.

Each well was ini t i~ly ischarged

vertically for a few hours to clear cuttings

from the well-bore prior to diverting the

good well planning and good well drilling programming and

management,This successful field development has been a com-

bined effort by ORMAT and some of the leading engineering

groups in the geothermal world:

PB

power of New Zealand,

Orkostufnon of Iceland and GeothermEx of the USA, s well

as the geothermal experts in various disciplines of KenGen

of

Tested Available Steam

I

Water

Proven Indiaative Capacity to Date wi th 1storderNCO Correation

to

4 April 2002

564

Olkaria III Field Development - Hagen Vs

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