nginx.conf から抜粋です。
log_format ltsv "time:$time_local"
"\thost:$remote_addr"
"\tforwardedfor:$http_x_forwarded_for"
"\tuser:$remote_user"
"\treq:$request"
"\tstatus:$status"
"\tsize:$body_bytes_sent"
"\treferer:$http_referer"
"\tua:$http_user_agent"
"\treqtime:$request_time"
"\tcache:$upstream_http_x_cache"
"\truntime:$upstream_http_x_runtime"
"\tapptime:$upstream_response_time"
"\tvhost:$host";
access_log logs/access.log ltsv;
項目は必要に応じて増減するといい感じ。