Gudao shallow gas field has been in later production period. In order to improve the development results, researches of reservoir characterization and enhancing gas recovery were launched in 1997. Utilizing technical measures including geology, geophysical, logging, gas reservoir engineering and stratigraphic correlation etc., original gas in place (OGIP) is recalculated and evaluated. On the basis of production characteristics analysis, distribution of remaining gas is made clear, and potential targets are put forward. The major results are as follows. 1. Substrata are re-divided utilizing sand tracing technique and secondary logging interpretation. 2. Cognition of some gas sands being not connected mutually is turned via stratigraphic re-correlation, thus contradictions of unbalanced reserves-production relationship and lower formation pressure of new wells than normal pressure are solved. 3. Change rules of output and pressure for various kinds of reservoirs are investigated, and main factors influencing recovery efficiency are analyzed and respective ways for enhancing recovery efficiency are brought forward sequentially. 4. OGIP is recalculated using pressure drop method (p/z-Gp) to verify results of volumetric method further, which can explain why recovery efficiencies of some reservoirs exceeded 100% before. 5. Based on break-even analysis, economic limit reserves for different kinds of reservoirs are computed, and overall adjustment plan is submitted, in which 12 wells have been brought on stream with gas rate of 107 × 103m3 /d.
Incremental producing reserves in place are 508 × 106m3with recoverable reserves 305 × 106m3, and favorable economic benefit has been seen with predictable production value about RMB 1,700 million Yuan. Thirty-five backup reservoirs are found as well, which provides dependable foundation for the future, and overall recovery efficiency predicted could be advanced for more than 5% and gas production decrease has been relieved. The results could provide certain directive meanings for gas fields of similar type.
The main purpose of reservoir characterization in later production period is to study the distribution rules of remaining gas, which has especial significance on maintaining field stable production and improving recovery factor. 1–4 Research of remaining gas distribution is based chiefly upon deepening understanding to reservoir geology, so as to find potential abundance areas of remaining gas, combining with analysis to performance data. 5–8
In Shengli Oil Fields, Gudao shallow gas field is one of the earliest gas fields put into production, as well as the biggest gas field among fields discovered presently, with cumulative gas production being 15% of that of Shengli approximately. Put into production in 1976, the field has been into later production period. Along with recovery percent of OGIP increasing, formation pressure declines year after year, and shut-in or low-deliverability wells increase with sand and/or water production being serious. In late 1996, there were only 14 gas wells producing normally among 46 wells, with gas rate of 71.3 *103m3/d (per-well gas rate 5.1 ??103m3/d only). Annual gas production was 6919 × 103m3 with a decline rate up to 21.8% in 1996. In order to improve production results, research of gas reservoir characterization and enhancing recovery factor was launched in 1997.
