introduction to geothermal well logging and testing

Sustainable Development Goals Short Course IV on Exploration and Development of Geothermal Resources

Felix Mwarania, Reservoir Engineer

INTRODUCTION TO GEOTHERMAL WELL LOGGING AND TESTING

23rd November, 2019

SDG Short Course IV on Exploration and Development of Geothermal ResourcesOrganized by UNU-GTP and KenGen | Lake Bogoria and Lake Naivasha | Nov 14-4 Dec, 2019

OUTLINE

• Introduction

• Well logging

• Conceptual models

• Well testing


GEOTHERMAL WELLS

Wells are vital in geothermal business. They provide;

• Access to energy extraction

• Information collection

Information from the wells is used in;

• Well siting

• Developing conceptual models

• As input for numerical models


WELL LOGGING

• Logging refers to continuous measurement carried out in boreholes

• The log shows changes in physical parameters measured as afunction of well depth

• The logs can be used to ‘estimate’ success of a well

• Parameters mostly logged in Olkaria geothermal field aretemperature and pressure


WELL LOGGING EQUIPMENT


WELL LOGGING – (COMPLETION TESTS AND HEAT-UP)

• Temperature and pressure logging • Pre injection Temperature/Pressure

• Injection tests• Multi-rate injection tests

• Injection Temperature/Pressure

• Pressure transient tests (pressure fall off)

• Temperature and pressure surveys• Conducted at regular intervals to monitor well recovery (1,4,7,14,21 and 28

days)


WELL LOGGING – TEMPERATURE PLOTS

Conductive profile:

• Observed in wells where rocks are impermeable

• Temperature increases linearly with depth


WELL LOGGING – TEMPERATURE PLOTS (2)

Convective profile:

• Depicts permeability in rocks

• Fluid motion controls temperature distribution.

• The profiles take a variety offorms, with isothermal sections,inversions, boiling sections or amixture


WELL LOGGING – PRESSURE PLOTS

• Injection profile Most useful in completion tests

• Gas pressure builds up when the well is shut and left to recover.

Gas rises until it is bled off or

Water level is depressed to theshallowest feed zone so that anyfurther gas is lost into theformation.


TEMPERATURE LOGS DURING INJECTION TESTS


TEMPERATURE PLOTS DURING INJECTION TESTS (2)


PRESSURE DURING INJECTION TESTS


TEMPERATURE CROSS-SECTION MAP

Temperature cross section – Eburru field


TEMPERATURE PLANAR MAPS - EBURRU

Temperature iso - map at 1000m a.s.lTemperature iso - map at 500m a.s.l


CONCEPTUAL MODEL - EBURRU

The information is used in developing conceptual model which explains;

• Heat source

• Upflow and outflow

• Recharge areas

From Eburru model

• Upflow is around EW-01

• Outflow at 1500 m a.s.l

• Cold recharge from all directions.


CONCEPTUAL MODEL - OLKARIA


CONCEPTUAL MODEL – OLKARIA (2)


WELL TESTING

Wells are monitored duringheat-up period by regular;

• water level or wellheadpressure measurement

• temperature recoverymeasurement

Once a well has heatedsufficiently, it is dischargetested to obtain informationon well productivity and fluidchemistry


METHODS TO STIMULATE FLOW IN WELLS

• Water level depression by pumping air using compressors

• Steam or two-phase injectionwhere a well is heated andpressurised using steam fromanother well

Because a well is difficult to start doesn’t mean that it is likely to be a poor producer.


WELL SET-UP IN KENYA


BRINE FLOW MEASUREMENT

• Common measuring methods• V-notch weir

𝑚 = 0.824 ∗ ℎ2.5∗ 𝜌

• Other methods• Timing

• Flow meters


STEAM FLOW MEASUREMENT

• Critical pressure measurement is common

• Uses Russel James formula


WELL TESTING INFORMATION

Shows how well dischargeparameters change underdifferent throttle conditions.

Data used to plot characteristiccurves

introduction to geothermal well logging and testing

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