Defining irreducible water saturation using global characteristics envelopes and novel correlations

Hoang²,

Bui³

et al. 2018

The APPEA Journal

The Laminaria field, located offshore in the Timor Sea, is one of Australia’s premier oil developments operated for many years by Woodside Energy Ltd. First production was achieved in 1999 using a state-of-the-art floating production storage and offloading vessel, the largest deployed in Australian waters. As is typical, dynamic reservoir simulation was used to predict reservoir performance and forecast production and ultimate recovery. Initial models, using special core analysis (SCAL) laboratory data and pseudos, covered a range of approaches, field and conceptual models. Initial coarser models also used straight-line relative permeability curves. These models were later refined during history matching. The success of simulation studies depends critically on optimal gridding, particularly vertical definition. An objective of the study presented is to demonstrate the importance of optimal and detailed vertical zonation using Routine Core Analysis data and a range of Hydraulic Flow Zone Unit models. In this regard, the performance of a fine-scale model is compared with three alternative, more traditional and coarse models. Secondly the choice of SCAL rock parameters may also have a significant impact, particularly relative permeability. This paper discusses the use of the more recently developed Carman-Kozeny based SCAL models, the Modified Carman-Kozeny Purcell (MCKP) model for capillary pressure and the 2-phase Modified Carman-Kozeny (2p-MCK) model for relative permeability. These models compare favourably with industry standard approaches, the use of Leverett J-functions for capillary pressure and the Modified Brooks-Corey model for relative permeability. The benefit of the MCK-based models is that they have better functionality and far better adherence to actual laboratory data.

The importance of optimal geological zonation and choice of rock parameters in dynamic reservoir simulation: a case study for the Laminaria field

Hoang²,

Bui³

et al. 2018

The APPEA Journal

Modelling of Drainage Capillary Pressure: Using the Modified Carman-Kozeny Purcell Model to Identify the Type of Pore Throat Distribution Inherent in Laboratory Data

Huu²,

Bui³

et al. 2016

All Days

Capillary pressure relationships (drainage) involve key SCA parameters measured in the laboratory. Reservoir engineers use capillary pressure relationships in reservoir engineering calculations and dynamic reservoir simulation and petrophysicists use such relationships in saturation-height modelling. The objective of this paper is to describe a novel technique to identify pore throat or grain size distributions from capillary pressure profiles. Capillary pressure, laboratory data are traditionally obtained from three different types of experiments: centrifuge, porous plate and mercury injection. The modified Carman-Kozeny Purcell (MCKP) model may be used in matching various laboratory results. Initial application of the MCKP model involved a standard matching procedure without differentiating according to the type of pore throat or grain size distribution. In this paper a refined, more powerful analysis technique is described in detail where matching of any laboratory data with the MCKP model is obtained in model space, showing various characteristics. Characteristic profiles observed in model space can be directly attributed to the type of pore throat or grain size distribution: homogeneous (narrow), broad (poorer sorting) and bimodal (two distinct distributions), or a mixture of distribution types. Comparison of model generated profiles with laboratory curves indicate a high degree of congruence, typically R2 > 0.99, consistently better than any other capillary pressure formulation. The technique is also able to pick up artefacts, such as a sample fracture or laboratory procedural issues. It is shown how the MCKP model may be used in predicting capillary pressure relationships from basic parameters by building a framework based on end-point correlations derived from available laboratory data. The paper presents various examples and a detailed case history for the Bayu-Undan gas field, covering various pore structure and diagenetic characteristics.

Capillary Pressure Drainage Curves: Modelling and Prediction of Capillary Entry Pressure

SPE/IATMI Asia Pacific Oil &Amp; Gas Conference and Exhibition

Kennaird²,

Bui³

et al. 2017

Capillary pressure (CP) measurements on core samples generally deploy one of three tests: porous plate (PP), centrifuge (CF) and mercury injection (MI). The first two mentioned tests are most often used to directly determine a CP relationship and the PP procedure most closely conforms to reservoir situations. CF test results may be superior for certain types of plugs and testing conditions, not to mention that testing is considerably faster. MICP tests are typically used for determining pore size distributions but may also be used to generate CP curves, with best results obtained by validation against the other two tests. MI tests also have the shortest timeline. CP curves have been modelled (fitted or matched) over the years with many alternative formulations, from the well-known J-function approach (Leverett, 1941) to more recent methods. Some formulations can realistically match the low pressures of CP profiles, including capillary entry pressure, while others do not cater for it at all. When the low-pressure part of CP curves exhibit a "roll-over effect (concave downward profile), entry pressure prediction may require high frequency data from MICP testing to give more definition. This paper examines several CP data sets, comparing PP and MI results, in light of pore throat distributions. Seven formulation are used to match entire CP profiles from PP data and are subsequentlyexaminedfor being able to represent capillary entry pressure. Various types of pore structures are discussed: homogeneous (narrow distribution), broad (poorer sorting) and bimodal (two distinct distributions) where the smaller pores are often related to pore-fill. It is shown that the Modified Carman-Kozeny Purcell (MCKP) formulation (Behrenbruch et al, 2011) is excellent in capturing the level of entry pressure for narrow pore throat size distributions or homogeneous plugs while entry pressure prediction for poorer sorted plugs tends to be less accurate, partially due to variation in samples.The detailed modelling of the roll-over effect requires a separate model. A new and improved correlation for (model) capillary entry pressure has been derived, showing results from Australian and other fields.