Abstract

The Minagish field has several reservoirs with oil accumulated primarily in lower Cretaceous Minagish Oolite -middle member (MMO) rocks. This giant carbonate hydrocarbon accumulation in the Minagish field was discovered in 1958 and accounts for > 80% of oil production in the Field. The Lower Minagish end member consists largely of clean to slightly argillaceous and/or carbonaceous fine grained peloidal packstones that were deposited in a low energy platform setting equivalent to very gently sloping outer ramp. Two significant flooding events divide the Lower Minagish Formation into three main productive zones upper, middle and lower. The contact between lower and middle member is an irregular one with a gradual diagenetic transition from limestone to tight dolostone. The Lower member has a gross pay of about 220ft above recorded lowest known oil (LKO) at about 10,000 feet tvdss close to the top of the Makhul carbonates (which forms the bottom seal of the reservoir). The recent conventional cores and image log data from the crest of the structure show that the Lower Minagish has faults and fractures which could provide permeability assist. There are 130 wells have been drilled in this field targeting Minagish Oolite (middle member); however 10 wells have recently been deepened to evaluate the oil potential of the Lower Minagish (LMN) and the underlying Makhul Formations. Five wells tested in the upper and middle zones have tested at production rates in the range of 400 to 4300 BOPD with the oil from the upper and middle zones having an API of 31° to 20.5°. This is significantly lower than the Minagish Oolite oil with an API range of 28° to 32°. This indicates probably a later reservoir filling than the Minagish Oolite oil emplacement. The discovery of this new oil is expected to enhance the STOIIP of the field. Although only wells in the northern block have been drilled and tested so far, the 3-D Seismic mapping suggests possible deeper oil down to in the southern block.

Introduction

The Minagish Field is located in the southwestern part of Kuwait (Fig. 1). It was discovered and began production in 1958. The field holds hydrocarbons in six major reservoirs ranging in age from Early Jurassic to Late Cretaceous. The Minagish Formation belongs to the lower part of the late Jurassic to Early Cretaceous Thamama Group, which is largely defined on sections in Saudi Arabia and the southern Gulf countries. The most precise age dating comes from a combination of calcareous nannofossils and calpionellids, although these were recovered only from the upper part of the Minagish Oolite to lower part of the Upper Minagish (Fig. 2a& 2b). The principal reservoir is the Lower Cretaceous MMO member which is contributing >80% of the fields production.

The discovery of new oil in the Lower Minagish (LMN) member is expected to significantly in crease production rates as well as estimates of original oil in place in Minagish Field. Production rates observed from wells tested in the reservoir, far exceeded what would normally be expected from reservoir with low matrix K (<1mD) as evidenced from core data. The Lower Minagish member consists largely of peloidal packstones that were deposited in low energy epeiric shelf or platform settings, equivalent to the outer ramp. There are 130 wells are penetrating the LMN reservoir. Most of these wells are partially penetrating while some penetrate through all the layers. Cores are available from 6 vertical wells, while acoustic images are available from 5 vertical wells and 1deviated well. (Fig. 2c) Fifty six wells have electrolog suites suitable for petrophysical analysis (Fig. 4). The porosity of this reservoir ranges between as low as 2–3% to as high as 22%. The rock and reservoir quality degrades toward the south of the field except locally areas in the southern and southwestern parts of Minagish where porosity is well developed. The 3-D seismic attributes are in agreement with the petrophysical interpretation of wireline logs. The permeability of the reservoir ranges between very low K (less than 1 mD) to medium K in the order of hundreds of mD.

The main aspects concerning Lower Minagish oil discovery are presented in this paper:

  • Structure and faults interpretation

  • Stratigraphy, depositional facies and its control on reservoir properties

  • Petrophysical modelling

  • OWC determination

  • Fracture analysis from image logs

  • Intergration of 3D-seismic data set

  • Pressure data analysis

  • Productional data analysis

  • Well test analysis

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