London Petrophysical Society - Prof. Paul Worthington Commemorative Webinar

Sessions: Abstracts (agenda to be finalised – talks below in no particular order,

schedule TBC)

Shaly Sands a la 1985

Alan Johnson – Integrated Petrophysical Solutions Ltd – Aberdeen

Paul Worthington published his seminal paper on shaly sand interpretation “The Evolution of

Shaly Sand Concepts in Formation Evaluation in 1985, 35 years ago.

In this paper, Paul labelled the period prior to 1950 as the “shale free” era. This would imply

that the, also, 35 years from 1950 to the publication of his paper, should be entitled the “shaly

sand” era. Of course we are still in that later period, but it is noteworthy that most of the

significant developments in the understanding and analysis of shaly sands happened in the

35 years from 1950 to 1985, with little substantial advance in understanding or in analysis

techniques evident since that time.

In his paper, Paul identified over 30 available shaly sand models available for the

petrophysicist of the day to choose from. His paper starts with a summary of the basic issues

encountered in the interpretation of electrical log measurements in shaly sands, he then

proceeds to examine and group the different models into common groups. For water-bearing

sands then groups are quite distinct: Vshale-based and Double Layer models. For hydrocarbon

bearing reservoir he identifies a further four generic groups.

In his critical discussion he identifies and discusses the common aspects, strengths, and

weaknesses of the different models but neither advocates nor condemns any particular

model. Having identified the limitations of each he goes on to suggest a path for future

developments, which, given the 35 years since its publication, have been disappointingly few.

This talk will review his approach to the shaly sand problem together with his grouping system

and thoughts on how the commonly adopted shaly sand, and others, fit into this and how well

they address the basic issues. It will go on to discuss, and suggest, further paths for

investigation of the still ongoing challenges.

Flow in porous materials: a tale of X-rays, minimal surfaces and wettability

Prof. Martin Blunt – Department of Earth Science & Engineering at Imperial College London

I will provide an overview of the current revolution in our understanding of flow, transport

and reaction processes in porous media, enabled by 3D imaging from the nanometre scale

upwards, microfluidics, and improved numerical methods. This will be illustrated by

examples from work at Imperial College London on multiphase flow in rocks with application

to carbon dioxide storage and oil recovery. X-rays are used to image flow processes in rocks

at a spatial resolution of down to 1µm and a time resolution between 1-1,000 s. These

experiments can be used to measure traditional multiphase flow properties – relative

permeability and capillary pressure – while providing pore-scale insight into displacement

processes. We show how an accurate characterization of wettability, or the local distribution

of contact angle, enables us to understand flow and trapping, and explain the circumstances

which are optimal for storage or recovery applications. The experiments also provide a

wealth of data to calibrate and validate pore-to-core scale flow and transport models.

The talk will end with a discussion of how the same ideas can be used to understand and

design processes in a wide variety of porous materials, including gas diffusion layers in fuel

cells and surgical masks.

Evaluating the hydrocarbon potential of carbonate reservoirs.

Brian Moss - Consultant petrophysicist, Mantra Petrophysics Limited, Fulham, London, UK.

The key paper:

Bust, V.K., Oletu, J.U. and Worthington, P.F. (2011). The Challenges for Carbonate

Petrophysics in Petroleum Resource Estimation. SPE 142819. Society of Petroleum Engineers.

(Whereas Paul is listed as the third author, the style and content attest to him being the chief contributor.)

This presentation summarises Paul’s views on recommended methodology for addressing the

challenges in quantifying the characterisation of carbonate reservoirs.

Central to the recommendations developed is recognising that, as carbonate pore systems

commonly comprise interparticle pores that coexist with complex intraparticle pores and

secondary pore systems such as dissolution voids and fractures, the greater degree of

inherent heterogeneity of carbonate reservoirs requires special treatment. Existing at all

scales, the heterogeneity poses challenges to data acquisition, petrophysical evaluation and

ultimately reservoir description/characterisation.

The essence of the methodology is that the carbonate petrophysics problem has 3 related

broad issues:

• recognition of log-identifiable rock types;

• establishment of partitioned datasets, each of which has an exclusive set of defined

interpretive algorithms;

• identification of net pay intervals.

The first issue is addressed by the extension of “electrolithofacies”, as used in clastic

reservoirs, to include the notion that variable pore geometry (texture and size distribution)

must be captured along with mineralogical information. The paper defines a term

“electroporefacies” as describing rock-fabric facies partitioned in terms of pore character. This

step may require non-standard logging tools.

The result of addressing the second issue would be a set of distinct equations or algorithms

to derive fluid saturation, predictive permeability and fluid saturation-height functions that

differentiate the one or more “petrofacies” present.

The solution to the third key issue follows from addressing the first two. Net pay is defined as

those intervals that show both storage of hydrocarbons and the capability for hydrocarbon

flow at economic rates – the same definition as for clastic reservoirs. Complications in

determining net pay in carbonates arise from pore system complexity together with a

tendency for the rock fabric to be of mixed-wettability.

The paper provides workflows for both log and core data that recognise coexisting

partitioning schemes for carbonate reservoirs.

Petroleum, Energy, and Electric Grid Analytics Learning Machine

Roger N. Anderson - Lamont-Doherty Earth Observatory, and the Data Science Institute,

Columbia University, New York, NY, USA

Petroleum, Energy, and Electric Grid Analytics Learning Machines (PALM™, EALM and EGALM)

all use a unique, machine learning based, “brutally empirical” analysis system. I will introduce

the methodology using PALM for use in upstream and midstream oil and gas field operations.

The objective of PALM is to become the go-to ‘brain’ for oil and gas exploration and

production, including drilling, completion, and pipeline gathering operations. PALM was

reduced to practice primarily in the unconventional shale oil and gas plays of the US.

PALM analyzed more than 200 attributes integrated from all available data referenced above,

in more than 200 horizontal wells and more than 4000 hydraulic fracture stages that were

drilled since 2012 in the wet gas region of the Marcellus shale of Pennsylvania and the

Midland Basin of the Texas Permian. PALM is a data-centric, computational learning and

predictive analysis system that uses open source algorithms combined with unique

techniques to increase production and reduce costs. For example, PALM predictive and

optimization technologies use time-series shape recognition and real-time decision trees to

steer hydraulic fractures to become more likely to produce high instead of low producers,

stage by stage and in real-time.

PALM also uses Support Vector Machines, logistic regression, Bayesian models, decision trees,

nearest neighbors, neural networks and deep learning networks uniquely combined to weigh

the importance of hundreds of geological, geophysical and engineering attributes, both

measured in the field and computed from theoretical analyses to enhanced production of oil,

gas, and natural gas liquids volumes and to minimize costs.

Ocean Drilling: petrophysics in a different world

Mike Lovell - School of Geography, Geology & the Environment, University of Leicester

Petrophysics is defined as…

“the study of the study of rock properties and their interactions with fluids (gases, liquid

hydrocarbons, and aqueous solutions)”

(Tiab and Donaldson, 1996)

There is no doubt that the hydrocarbon industry initiated the study of petrophysics, first

through electrical coring or, as we now know it, downhole logging (Schlumberger, 1927), and

then through quantitative analysis (Archie, 1942). Since then the industry has subsequently

underpinned, developed and maintained the subject, almost exclusively as its own.

But there is another side to petrophysics, and that is its use outside of hydrocarbon

exploration, principally in the world of ocean drilling. Initially used on an ad hoc basis, the

renewal of the programme in the early 1980s brought about the introduction of routine

downhole measurements to complement laboratory analyses on core. This development –

making downhole logging central to the biggest international geoscientific research

programme on Earth - was brought about through the intervention of several key players, one

of whom was Paul Worthington, and petrophysics continues in ocean drilling to this day,

though not without significant recurring struggles within the scientific community.

Separate to this significant contribution to academic research, is the legacy Paul leaves,

brought about through his careful reviews of petrophysics papers on different topics, distilled

into thoughtful and erudite summaries that not only informed but also provoked discussion.

These review papers form a welcome entry point into the world of petrophysics… …a subject

characterised by a lack of a unique vocabulary. In petrophysics, people use different words to

describe the same thing, and the same word to describe different things. It can be very

frustrating.

As Humpty Dumpty tells Alice in Wonderland…

“When I use a word,’ Humpty Dumpty said in rather a scornful tone, ‘it means just what I

choose it to mean — neither more nor less.’

’The question is,’ said Alice, ‘whether you can make words mean so many different things.’

Paul Worthington’s many review papers attempt to put an end to this dichotomy and realise

a vocabulary that enables communication and dialogue, and as such should be welcomed as

a starting point for further discussion. Numerous students and practitioners of petrophysics

have appreciated them, whether in academia or industry.

References:

Carroll, Lewis. 1897 [1872]. Through the Looking Glass and What Alice Found There.

Tiab, D, and Donaldson, E. (1996). Petrophysics: theory and practice of measuring rock and fluid transport

properties. Gulf Publishing Company, Houston. 706pp.

Trials, tribulations and confessions of a LWD log analyst.

Iwan “Bob” Roberts

LWD data “issues”, their explanation, avoidance, mitigation and repair

LWD logging is long established as a mainstream source of open hole well data for a wide

range applications of interest to geoscientists. The reliability of LWD measurements, while

greatly improved over the last few decades, inevitably falls short of perfection due to many

factors including human error at various junctures of the data acquisition processes, data

transmission errors, tool failures, physical limitations of measurements, environmental

factors and anomalous or challenging formations.

As a field engineer and later a log analyst with a major LWD service provider the author

encountered many of the possible modes of failure and data discrepancies of all kinds and

was tasked with diagnosing the issues leading to the data discrepancy and “fixing” them,

whether by reprocessing, correcting, editing or in some cases re-logging the interval.

It is often necessary to diagnose such issues as and when they occur based on realtime data

which is usually incomplete (since only a subset of the raw data can be transmitted to surface

due to bandwidth limitations). It is thus not always immediately obvious whether an

unexpected response is wholly spurious, requiring an expensive round trip out of the hole, or

whether it can be explained by formation properties, borehole environment or perhaps as an

issue only affecting the realtime data that would not affect the recorded memory data. In

such instances it may be unnecessary to consume rig time on a trip and drilling may be

continued. Diagnosis is assisted by tool status and other ancillary data that may highlight

deviations from ideal engineering parameters or tool specifications that can help to explain

or eliminate cause

After diagnosis, a plan to mitigate further recurrence of the issue may be appropriate, and

remedial measures such as recalibrating a tool, reprocessing of data, recovery of lost data can

sometimes rescue a previously unpromising looking log. On other occasions, it has been

possible to show that a “failure” was nothing of the kind and that the measurement response

was correct.

The presentation will take you “under the hood/bonnet” of LWD measurements and explain

some of the common and uncommon issues encountered.

Net Pay Cut-Offs – A Rigorous Approach

Alan Johnson – Integrated Petrophysical Solutions Ltd – Aberdeen

Bob Harrison – Soluzioni Idrocarburi s.r.l.

In two SPE papers, the first: “The Role of Cut-offs in Integrated Reservoir Studies” co-authored

by Luca Cosentino and published in 2005 and second: “The Application of Cut-offs in

Integrated Reservoir Studies” published in 2008, Paul Worthington proposed and developed

what he intended to be a non-subjective methodology and work-flow for the definition of net

pay and net/gross.

He followed these papers by a further, and relatively more accessible, one in 2010, “Net Pay

– What Is It? What Does it Do? How do we Quantify It? How Do We Use It?” again published

by SPE. In this he summarised the approach defined in the first two papers, but expanded on

this to discuss the practical application and how far these be applicable particular

circumstances: Thinly Laminated, Stacked, Naturally Fractured, Tight Gas and Coal Bed

Methane reservoirs. He also suggested a workflow by which cut-offs may possibly be applied

at the geocellular level and reviewed applications in deviated and horizontal wells.

Throughout these papers he advocated the definition of Net Pay, as opposed to the static

parameters of Net Sand or Net Reservoir, as an input to the ultimate definition of recoverable

reserves. In this he suggested an approach, labelled “dynamic conditioning” of cut-offs. In this

he proposed defining cut-offs aligned with the envisaged depletion mechanism in a particular

reservoir. For primary depletion (e.g. gas) reservoirs He advocated using a cut-off based on

Leverett’s “equivalent circular pore diameter” ((k/φ)0.5) while in waterflood situations he

suggested one based on end-point relative permeability. In the proposed workflow, these cut-

offs are related, via air permeability, back to static, log-derived parameters of Vshale, porosity

and water saturation.

This talk will present a detailed review of Paul’s conceptual framework and proposed

methodologies while also highlighting some of the outstanding limitations in their practical

application, which still need to be addressed.

The Future of Petrophysics – a triptych of complementary visions

Michel Claverie - Independent

“It’s tough to make predictions, especially about the future.” Attributed to Yogi Berra (1925-

2015), New York Yankees catcher, manager, and inadvertent philosopher.

Paul Worthington was kind enough to write a paper for the SPWLA Petrophysics Journal at

very short notice upon my invitation – I was at the time its stressed Editor with an impending

deadline. The paper, “The Direction of Petrophysics: a Perspective to 2020” was published in

SPWLA Petrophysics Vol. 52 No. 4, Aug-2011.

My Editor’s column for the issue included:

[…]

The first paper is a contribution from Paul Worthington, “The Direction of Petrophysics: a

Perspective to 2020”.

Paul presented this topic as an invited speaker at the Colorado Springs Annual Symposium in

May, and graciously accepted to expand his lecture into a full article, at very short notice, to

provide the readers of Petrophysics who could not attend the symposium an up-to-date and

comprehensive picture of the state and future of petrophysics. Although all who attended

Paul’s talk thoroughly enjoyed the flow of ideas and the challenges he presented, Paul’s work

is even better served by the written word, where his elegant native English style effortlessly

carries his rigorous and innovative message. Having experienced his well-structured

sentences and his precise vocabulary, the reader of Paul’s prose usually pauses at the end of

the paper, puts down the English dictionary (unabridged version), and exclaims “I couldn’t

have said that better myself!”. And that is probably true.

In this paper, Paul defines the current status of petrophysics and its driving forces; he

proposes a proactive response for petrophysics to address the reservoir complexity and

interpretation challenges, and to ensure the effective use of technology, through the twofold

strategy of a “scenario approach” and a “key-well concept”; he describes petrophysical

responses for achieving data integrity and matching databases to reservoir complexity, to

reconcile scales of measurement, for sampling anisotropic and heterogeneous reservoirs,

improve net and pay reservoir evaluation, and expose hidden pay. Paul then defines fit-for-

purpose formation evaluation for problematic reservoirs such as clastic thin beds, shaly,

freshwater and high capillarity reservoirs, carbonates, and tight gas, shale gas and coal bed

methane reservoirs. Finally, Paul expects that in 2020, reservoirs will be problematic, and we

will have to contend with sour and volatile hydrocarbons, high pressure and temperature,

geomechanical instability in depleted reservoirs, and the specific needs of horizontal wells.

The greatest challenge to petrophysicists, however, will be to select and acquire the

appropriate datasets needed to evaluate these complex reservoirs.

[…]

Geoscience petrophysics

Paul’s paper represents the expert vision of the geoscience petrophysicist – related to field

studies. Of course, Paul accumulated a vast operator’s experience as the Chief Petrophysicist

for BP, but I think that the strategy he offers in his 2011 paper relates to petrophysics as a

geoscience.

Ten years after this 2011 publication, the technology and the evaluation methods described

by Paul are all available, but they are underused, to the lasting detriment of formation

evaluation accuracy in many current wells.

Operations petrophysics

Another, more recent, expert vision of the future of petrophysics is provided by Tim Pritchard

in his short but highly insightful essay “The Future of Petrophysics”, published in the SPWLA

London Newsletter of April 2017. He offers 7 precepts that represent the concerns of the

operations petrophysicist, based on his extensive experience as the Chief Petrophysicist for

BG, responsible for formation evaluation of specific oil & gas fields:

• formation evaluation needs to keep pace with ever developing technology

• the work of the petrophysicist, reservoir engineer and modeller are ever more

integrated

• geomechanics must be integrated into reservoir models

• rock physics should integrate upscaled petrophysical properties with imaging

technologies

• utilise embedded sensors for production optimization

• environmental management: adopt the technology to assure well integrity

• implement a focused strategy to take advantage of technology developments

He concludes that “perhaps the most insightful comment is that the best way to predict the

future is to create it”, and predicts that “those organisations [that do] will deliver a stronger

commercial performance in the new world of low gas/oil prices”.

Measurements & services petrophysics

Music to the ears for the 3rd character of this triptych of complementary visions: the

measurements & services petrophysicist.

For her, petrophysics services consist in a matrix of elements that characterize a product and

its delivery. The measurements & services petrophysics services should provide

• accurate formation evaluation in any reservoir of interest

• match customer requirements & practices, and outperform competition capabilities

• leadership technology of hardware & software, and domain expertise

• efficient acquisition in a large range of well conditions

• stand-alone and combined domains applications – robust, consistent & innovative

The elements that describe the future of measurements & services petrophysics appear quite

different to those listed for geoscience and operations petrophysics, but the 3 activities are

involved in a tight symbiotic relationship - neither of them can exist without the others.

So, how are new petrophysics services planned and constructed for the future? Since they

cannot be constructed to match the exact specifications of every reservoir properties, well

conditions, or elements from the matrix, they must be highly adaptable. In fact, the individual

visions for geoscience petrophysics and operations petrophysics matter less than the ability

of measurements and services petrophysics to adapt to, and (better) to anticipate variability

and changes.