SECTION 4 - Well Test Analysis 4.1 Crystalline Basement Tests..............................................................................................29 4.2 Lower Cretaceous Sand Tests.........................................................................................29 4.3 Upper Cretaceous (Campanian) Sand Tests................................................................32 4.4 Post Reperforation Tests - All Sedimentary Intervals................................................35 4.5 Post Reperforation Tests - Upper Cretaceous (Campanian) Sand Only ...............37
SECTION 5 - Temperature Survey Interpretation 5.1 Temperature Survey Interpretation.................................................................................39
Lunds Energi AB
Dept. of Engineering Geology.LTH.
SECTION 6 - Well Deliverability 6.1 Well Deliverability Tests........................................................................................................45
Lunds Energi AB
Section
Dept. of Engineering Geology.LTH.
1
INTRODUCTION 1.1
Background
The Lund DGE#1 Deep Geothermal Well has been developed by Lunds Energi AB and the Department of Engineering Geology at Lund Institute of Technology. The well was drilled over the winter of 2002/2003 to a total depth of 3701.8 m The well encountered crystalline basement at 1950 m and penetrated a total of 1750 m of this formation. Initially the plan had been to set 13⅝” casing in the top of the crystalline basement and leave the entire crystalline basement as an open hole section. However, the drilling contractor became stuck at 3365m necessitating the setting of a 9⅝” liner to 3310 m and side-tracking the well just above 3200m. Prior to running the 9⅝” liner, the open hole section from 1975 to 3365 m was logged and flow tested. Production rates were disappointing at around 0.2 m3/min with the wellbore fully evacuated by air; similarly, injection rates of around 0.2 m3/min were achieved at an injection pressure of around 100 bar. After the well had been drilled to 3701.8 m the open hole section from 3198 to 3701.8 m was logged and flow tested. Similar results were obtained to those seen in the upper crystalline basement section. During the drilling of the crystalline basement, evidence of extensive fracturing and rock shattering were observed in both the cuttings samples and the wireline logs. The flowrates achieved from the crystalline basement do not appear to be consistent with the observed extensive fracturing.
1.2
Well Evaluation Program
The Well Evaluation Program has been designed to: • • • •
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Acid stimulate two intervals in the open hole crystalline basement which were identified as having contributed to flow during the prior flow tests. Flow test the crystalline basement open hole section Perform an injection test on the crystalline basement open hole section Perforate three intervals 3125 to 3135 m, 2935 to 2945 m and 2750 to 2760 m in the cased hole crystalline basement section which displayed high temperature spikes while running a PLT during an earlier flow period before casing was set, and flow test these intervals. Perforate three intervals 1895 to 1905 m, 1867 to 1872 m and 1827 to 1841 m in the cased hole sedimentary section, adjacent to clean sands with good porosity, and flow test these intervals. Perforate 1500 to 1525 m, which represents the lower quarter of 100 m massive sand from 1427 to 1528 m displaying exceptional porosity, and flow test this interval. 1
Lunds Energi AB
Section
2
Executive Summary 2.1
Executive Summary
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There are two discreet and hydraulically isolated production zones in the Lund DGE#1 sedimentary section – the Campanian at 1427-1528 m, and the Lower Cretaceous sands at 1827-1853 and 1895-1905 m.
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The Campanian produces water at around 35oC and the Lower Cretaceous at 45oC.
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Production from the two sand intervals is likely to be compromised by the nonideal completion and the necessity to perforate through two strings of casing and two cement sheaths as the possibility of using these Cretaceous Sands was not evident from the geological prognosis.
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Furthermore, as the prevention of potentially damaging mud filtrate invasion was not a priority whilst drilling the sedimentary section of this well.
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On test the Campanian section produced at a final rate of 52 l/sec, and the Lower Cretaceous sands produced at 35 l/sec over 12 hours. Combined maximum flow rate was 64.5 l/sec.
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Only around 47 m of the 101 m Campanian sand is contributing to production, and this coincides with the interval that was perforated with a 50 bar underbalance. The 45 m section of this interval which was perforated in a balanced situation, together with other intervals which were perforated balanced, failed to contribute significantly to flow. Perforating underbalanced is clearly favourable to improved flow.
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Flow and pressure build-up analysis on the Campanian sand indicates the presence of a natural fracture system, which is no doubt a result of the tectonic activity in this area.
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Flow and pressure build-up analyses on the Lower Cretaceous sands show evidence of skin damage, which should be removed in a properly designed completion.
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Deliverability analysis indicates that flow rates of 80 to 100 l/sec are achievable in this well, albeit at relatively high drawdowns (dynamic fluid level at 425 to 500 m below surface). These rates are likely to be achieved at lower drawdowns with a mud program designed to minimise mud filtrate invasion and maintain native rock properties, together with an optimally designed completion.
